Ligands for imaging cardiac innervation

ABSTRACT

Novel compounds that find use as imaging agents within nuclear medicine applications (PET imaging) for imaging of cardiac innervation are disclosed. These PET based radiotracers may exhibit increased stability, decreased NE release thereby reducing side effects, improved quantitative data, and/or high affinity for VMAT over prior radiotracers. In some instances the compounds are developed by derivatizing certain compounds with 18F in a variety of positions: aryl, alkyl, a keto, benzylic, beta-alkylethers, gamma-propylalkylethers and beta-proplylalkylethers. Alternatively or additionally, a methyl group a is added to the amine, and/or the catechol functionality is either eliminated or masked as a way of making these compounds more stable.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No. 13/916,205, filed Jun. 12, 2013, entitled “LIGANDS FOR IMAGING CARDIAC INNERVATION”, which is a Continuation of U.S. application Ser. No. 12/448,575, filed May 14, 2010, entitled “LIGANDS FOR IMAGING CARDIAC INNERVATION”, which is a national stage filing under 35 U.S.C. 371 of International Patent Application Serial No. PCT/US2007/088500, filed Dec. 21, 2007, entitled “LIGANDS FOR IMAGING CARDIAC INNERVATION”, which is a Non-Prov of Prov (35 USC 119(e)) of U.S. application Ser. No. 60/877,211, filed Dec. 26, 2006, entitled “LIGANDS FOR IMAGING CONGESTIVE HEART FAILURE”. The entire contents of these applications are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

Novel compounds that find use as imaging agents within nuclear medicine applications (e.g., PET imaging and SPECT imaging) are disclosed. Methods of using the compounds to image cardiac innervation are also provided.

BACKGROUND OF THE INVENTION

Heart failure (HF) is a condition that afflicts increasingly more people each year. This condition is defined as the common end-stage of many frequent cardiac diseases (e.g. myocardial infarction, pressure overload, volume overload, viral myocarditis, toxic cardiomyopathy), and is characterized by relentless progression. The resultant myocardial damage from such events in conjunction with neurohormonal and cytokine activation, is suspect for the causes of chamber remodeling of the heart, an initial phase of HF. Early diagnosis of HF is difficult because the remodeling process precedes the development of symptoms by months or even years. The current diagnostic tests (e.g. two dimensional echocardiogram coupled with Doppler flow studies) only reveal changes in the heart in the late stages of the disease. To date, no cure for HF exists. Early diagnosis is a key factor in achieving a good prognosis and management of this disease.

An imaging agent that identifies patients in early HF would enable immediate treatment and life-style improvements for those living with this disease. In the past, researchers have investigated a variety of biological markers found in HF to develop methods for detection of early stages of HF. The cardiac sympathetic nervous system (CSNS), which is part of the autonomic nervous system, was found to be one of the biological markers of interest.

The autonomic nerve system, which plays a crucial role in regulating cardiac function, consists of the CSNS and the cardiac parasympathetic nervous system (CPNS). In the two branches of the cardiac autonomic innervations, the CSNS and CPNS, postganglionic sympathetic neurons communicate with each other via the neurotransmitter norepinephrine (NE). These branches work in finely tuned opposition to each other in the heart. Thus stimulus to the sympathetic nerve system causes increased contractility, acceleration of heart rate and conduction, which is mediated by the action of NE on post synaptic β₁ adrenoceptors. Stimulation of the parasympathetic nerves on the other hand, leads to a decrease in heart rate and conduction. This is mediated by action of acetylcholine on postsynaptic M₂ muscarinic acctylcholine receptors.

NE is the neurotransmitter of postganglionic sympathetic neurons. NE is stored in vesicles within the neurons and is released by Ca⁺² mediated exocytosis into the synaptic cleft upon nerve depolarization. Most of the norepinephrine released is returned to the neuron by the norepinephrine transporter (NET; also known as “Uptake-1” mechanism) and repackaged into storage vesicles by the vesicular monoamine transporter (VMAT). The remaining amount of NE in the synaptic cleft binds to postsynaptic β1 adrenoceptors controlling heart contractility, acceleration of heart rate and heart conduction. Tissue concentrations of NE in the normal heart are generally considered to be reliable markers of regional sympathetic nerve density, which are uniformly distributed throughout the heart.

Abnormalities in cardiac innervation have been implicated in the pathophysiology of many heart diseases, including sudden cardiac death, congestive heart failure, diabetic autonomic neuropathy, myocardial ischemia and cardiac arrhythmias. Heart failure is characterized by a hyperadrenergic state whereby increased systemic levels of NE and increased local spillover of catecholamines occurs. It has been documented that there is a reduction in cardiac uptake-1 density or function in tissue samples of both human patients and animal models, which may be the reason for the increased amount of systemic NE observed in myocardium tissue. Development of methods to assess physiological changes of NE uptake-1 in the myocardium are therefore highly desirable.

As disclosed in United States Patent Application Publication No. 20060127309 (herein incorporated by reference in its entirety), medical radionuclide imaging (e.g., Nuclear Medicine) is a key component of modern medical practice. This methodology involves the administration, typically by injection, of tracer amounts of a radioactive substance (e.g., radiotracer agents, radiotherapeutic agents, and radiopharmaceutical agents), which subsequently localize in the body in a manner dependent on the physiologic function of the organ or tissue system being studied. The radiotracer emissions, most commonly gamma photons, are imaged with a detector outside the body, creating a map of the radiotracer distribution within the body. When interpreted by an appropriately trained physician, these images provide information of great value in the clinical diagnosis and treatment of disease. Typical applications of this technology include detection of coronary artery disease (e.g., thallium scanning) and the detection of cancerous involvement of bones (e.g., bone scanning). The overwhelming bulk of clinical radionuclide imaging is performed using gamma emitting radiotracers and detectors known as “gamma cameras.”

Recent advances in diagnostic imaging, such as magnetic resonance imaging (MRI), computerized tomography (CT), single photon emission computerized tomography (SPECT), and positron emission tomography (PET) have made a significant impact in cardiology, neurology, oncology, and radiology. Although these diagnostic methods employ different techniques and yield different types of anatomic and functional information, this information is often complementary in the diagnostic process. Generally speaking, PET uses imaging agents labeled with the positron-emitters such as ¹⁸F, ¹¹C, ¹³N and ¹⁵O, ⁷⁵Br, ⁷⁶Br and ¹²⁴I. SPECT uses imaging agents labeled with the single-photon-emitters such as ²⁰¹Tl, ⁹⁹Tc, ¹²³I, and ¹³¹I.

Glucose-based and amino acid-based compounds have also been used as imaging agents. Amino acid-based compounds are more useful in analyzing tumor cells, due to their faster uptake and incorporation into protein synthesis. Of the amino acid-based compounds, ¹¹C- and ¹⁸F-containing compounds have been used with success. ¹¹C-containing radiolabeled amino acids suitable for imaging include, for example, L-[1-¹¹C]leucine, L-[1-¹¹C]tyrosine, L-[methyl-¹¹C]methionine and L-[1-¹¹C]methionine.

PET scans involve the detection of gamma rays in the form of annihilation photons from short-lived positron emitting radioactive isotopes including, but not limited to ¹⁸F with a half-life of approximately 110 minutes, ¹¹C with a half-life of approximately 20 minutes, ¹³N with a half-life of approximately 10 minutes and ¹⁵O with a half-life of approximately 2 minutes, using the coincidence method. For PET imaging studies of cardiac sympathetic innervation, carbon-11 (¹¹C) labeled compounds such as [¹¹C]meta-hydroxyephedrine (HED) are frequently used at major PET centers that have in-house cyclotrons and radiochemistry facilities. Recently the nuclear medicine market has seen a substantial increase in stand-alone PET imaging centers that do not have cyclotrons. These satellite-type facilities typically use 2-[¹⁸F]fluoro-2-deoxy-D-glucose (FDG) for PET imaging of cancerous tumors.

SPECT, on the other hand, uses longer-lived isotopes including but not limited to ^(99m)Tc with a half-life of approximately 6 hours and ²⁰¹Tl with a half-life of approximately 74 hours. The resolution in present SPECT systems, however, is lower than that presently available in PET systems.

Radiotracers targeting each branch of cardiac autonomic innervation have been developed. The number of tracers developed for the sympathetic neurons however is far more than those developed for the parasympathetic neurons. There are two reasons for this. First, the NET is nonselective and will readily transport structural analogs of NE into the sympathetic varicosity. The choline uptake carrier on the other hand is highly selective. Second, there is a dense population of the sympathetic nerves in the left ventricular wall as compared to the parasympathetic neurons found in the thin walls of the atria and conduction nodes. This has therefore, made imaging the sympathetic neurons easier. The structures below are examples of radiolabel led catecholamines and catecholamine analogues, and guanadines used for studying cardiac sympathetic neurons.

Radiolabelled Catecholamines and Catecholamine Analogues, and Guanidines Used for Studying Cardiac Sympathetic Neurons

[¹¹C]Dopamine ([¹¹C]DA) and 6-[¹⁸F]fluorodopamine (6-[¹⁸F]FDA) have been used to image dogs and baboons respectively. 6-[¹⁸F]FDA showed rapid uptake and clearance, and good images of the heart. [¹¹C]Norepinephrine ([¹¹C]NE) has been used to obtain planar images of canine heart and clearly visualized the left ventricular myocardium in a cynomologous monkey. 6-[¹⁸F]Fluoronorepinephrine (6-[¹⁸F]FNE) has also been used to image the baboon heart and showed high uptake and retention. Myocardial kinetics of [¹¹C]epinephrine ([¹¹C]EPI) has been extensively studied and is handled in a similar manner to NE and has been used to assess neuronal changes in cardiac transplant patients.

The catecholamine analogues like 1R,2S-6-[¹⁸F]-fluorometaraminol (6-[¹⁸F]FMR), [¹¹C]hydroxyephedrine ([¹¹C]HED) and [¹¹C]phenylephrine ([¹¹C]PHEN) have also been used very effectively to study the sympathetic nerve system. [¹²³]-meta-Iodobenzylguanidine (MIBG) is another extensively studied catecholamine analog that shows neuronal uptake as well as uptake by the cardiac myocytes, when studying sympathetic nerve fibers of the heart. Studies with MIBG allow clinicians to map the regional distribution of nerve fibers in the heart using imaging devices found in all nuclear medicine clinics. MIBG is also used for diagnostic imaging and radiotherapy of adrenergic tumors, such as neuroblastoma and pheochromocytoma. [¹²³I]MIBG has been used to delineate nerve damage while [¹¹C]HED has been used to demonstrate neuronal abnormalities in a number of heart conditions including transplanted hearts, cardiomyopathy, acute myocardial infarction and cardiac diabetic neuropathy. MIBG is a SPECT tracer, however, and therefore does not provide quantitative information.

Lastly, [¹²⁵I]-CAAP was the first ¹²⁵I-radiolabeled 1-carboxamidino-4-phenyl-piperazine. Comparison studies of [¹²⁵I]-CAAP with [¹²⁵I]-MIBG in tissue distribution studies in rats demonstrated equivalent uptake of the radiotracer in heart tissue. The uptake and retention of the compounds in the myocardium tissue are speculated to be due to the same mechanism of action, which recognizes the guanidine functionality in both substrates. NET uptake-1 is a possible mode of action. Several positron emitting radiotracers were therefore developed as shown below.

MIBG and Positron Emitting Analogues

Of the three benzylguanidine PET tracers developed only one, 4-[¹⁸F]fluoro-3-iodobenzylguanidine ([¹⁸F]FIBG) demonstrated uptake and behavior similar to MIBG in vivo.

All the tracers mentioned above give valuable information but have their limitations. These include metabolic instability (NE, FNE, DA, FDA, PHEN, EPI and CAAP) or pharmacologically active norepinephrine release (FMR). MIBG also has its drawbacks. It has considerable extraneuronal uptake mediated by passive diffusion and by the uptake-2 (membrane transport) mechanism. And, being a SPECT agent, like CAAP, MIBG does not give quantitative information and has other associated limitations. There is therefore a need for tracers that will show the following characteristics:

a) stability,

b) not cause NE release (thereby reducing side effects),

c) give quantitative information, and/or

d) high affinity for VMAT.

SUMMARY OF THE INVENTION

The present invention provides novel compounds that find use as imaging agents within nuclear medicine applications (e.g., PET imaging and SPECT imaging). Methods of using the compounds to image cardiac innervation are also provided. In some embodiments of the present invention, the PET based radiotracers exhibit increased stability, decreased NE release (thereby reducing side effects), improved quantitative information, and/or high affinity for VMAT. In certain embodiments, these tracers are based on compounds that are derivatized with ¹⁸F in a variety of positions: aryl, alkyl, a keto, benzylic, beta-alkylethers, gamma-propylalkylethers and beta-proplylalkylethers, as shown in their structures below. In alternative embodiments, a methyl group α is added to the amine, and/or the catechol functionality is either eliminated or masked as a way of making these molecules more stable.

One embodiment of the present invention provides PET based radiotracers as illustrated in the general structure I:

wherein m=0, 1, or 2; n=0, 1, 2, and A is O or absent. R, R₁, R₂, and R₃ are independently selected from the group consisting of H, OR₄, F, Cl, CF₃, Br, 1, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₄, CO₂R₄, N(R₄)₂, CN, C(═NH)NHR₅, C(═O)NHR₅, NHC(═O)NR₅, NHNR₅, SO₂OR₅, and imaging moiety Im. Q consists of bridging groups that can be present between Y and Z, and to R₂. The Q bridging groups can independently be selected from the group consisting of CH₂, CH, CR₅, N, NH, NR₅, O and S in such a combination as to create a chemically stable structure. The substituents W, X, Y and Z may independently be selected from the group consisting of H, OR₄, N R₄, F, Cl, Br, I, Im, aryl, and heteroaryl. R₄ and R₅ may be H, alkyl, aryl or heteroaryl substituents. In an alternative embodiment, the alkyl, aryl or heteroaryl substituents may be substituted with various functional groups as hereinafter described.

In certain embodiments, the present invention provides a PET based radiotracer having structure II as follows:

wherein linking groups B, D, E, F, and G are independently selected from the group consisting of a bond, alkyl (C₁-C₅; preferably C₂), aryl, aralkyl, alkylaryl, heteroaryl, alkoxy, alkylamino, aminoalkyl, aryloxy, alkoxyalkyl, thioalkyl, and heterocyclyl. R₆ through R₁₂ are independently selected from the group consisting of H, OR₄, F, Cl, CF₃, Br, I, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₄, CO₂R₄, N(R₄)₂, CN, C(═NH)NHR₅, C(═O)NHR₅, NHC(═O)NR₅, NHNR₅, SO₂OR₅, and imaging moiety Im. R₄ and R₅ may be H, alkyl, aryl or heteroaryl substituents. And, Im is selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, ^(99m)Tc, ¹⁵³Gd, ¹¹¹In, and ⁹⁰Y.

In certain embodiments, the present invention provides a PET based radiotracer compound having the following Structure Alpha:

wherein n=0, 1, 2, 3 and A is O or absent. R, R₁, R₂ and R₃ are independently selected from the group consisting of H, OR₄, F, Cl, Br, I, CF₃, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₄, CO₂R₄, N(R₄)₂, CN, C(═NR₄)OR₅, NR₄(C(═NR₅)NHR₆, C(═NR₄)NHR₅, C(═O)NHR₄, NR₄C(═O)NR₅, NR₄NR₅, SO₂OR₄, and Im. The substituents W, X, Y and Z can independently be selected from the group consisting of H, OR₄, N(R₄)₂, F, Cl, Br, I, CF₃, Im, aryl, and heteroaryl. R₄, R₅, and R₆ are H, alkyl, aryl or heteroaryl substituents. And, the imaging moiety, Im, can be selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, ¹³¹I, ^(99m)Tc, ¹⁵³Gd, or ¹¹¹In.

In addition, in a further embodiment, the invention also provides a PET radiotracer compound having Structure Beta:

wherein n=0, 1, 2, 3 and A=O or is absent. R, R₁, R₂ and R₃ are independently selected from the group consisting of H, OR₄, F, Cl, Br, I, CF₃, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₄, CO₂R₄, N(R₄)₂, CN, C(═NR₄)OR₅, NR₄(C(═NR₅)NHR₆, C(═NR₄)NHR₅, C(═O)NHR₄, NR₄C(═O)NR₅, NR₄NR₅, SO₂OR₄, and Im. The substituents W and X can independently be selected from the group consisting of H, OR₄, N(R₄)₂, F, Cl, Br, I, CF₃, Im, aryl, and heteroaryl. Y and Z can be selected from the group consisting of CH, CH₂, O, N, NR₇, and CH═CH. Bridging group Q is absent or selected from the group consisting of CH, CR₄, CH₂, N, NR₄, NH, S, and O. R₄, R₅, and R₆ are H, alkyl, aryl or heteroaryl substituents.

In certain embodiments, the present invention provides a PET based radiotracer having Structure Chi as follows:

wherein R through R₂ are independently selected from the group consisting of H, OR₃, F, Cl, Br, I, CH₂F, OCH₂CH₂F, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₃, CO₂R₃, and Im. Im is a imaging moiety and is selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, and ¹³¹I. R₃ can be an H, alkyl, aryl or heteroaryl substituent.

In certain embodiments, the present invention provides a PET based radiotracer having Structure Delta as follows:

wherein linking groups B, D, E, F and G are independently selected from the group consisting of a bond, alkyl (C₁-C₅; preferably C₂), aryl, aralkyl, alkylaryl, heteroaryl, alkoxy, alkylamino, aryloxy, and alkoxyalkyl. R₈ through R₁₄ are independently selected from the group consisting of H, OR₃, F, Cl, Br, I, CH₂F, OCH₂CH₂F, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₃, CO₂R₃, and Im. R₃, R₄, R₅, and R₁ can independently be selected from the group consisting of H, alkyl, aryl, aralkyl, heteroaryl, alkylamino, alkyloxy, and aryloxy. The imaging moiety, Im, can be selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, ¹³¹I, ^(99m)TC, ¹⁵³Gd, and ¹¹¹In.

A preferred embodiment describes the PET based radiotracer compound N-[3-bromo-4-(3-[¹⁸F]fluoropropoxy)-benzyl]-guanidine hydrochloride, as illustrated in Structure Epsilon below:

A further embodiment describes a method of imaging cardiac innervation comprising the steps of: administering an effective amount of one or more of the compounds disclosed above, to a patient; detecting gamma radiation emitted by said compound; and forming an image therefrom.

The present invention is directed to these, as well as other important ends, hereinafter described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first series of representative cardiac short- and long-axis images in a non-human primate according to an embodiment of the invention.

FIG. 2 is a second series of cardiac short- and long-axis images in a non-human primate according to a further embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS Definitions

Unless otherwise indicated, the term “lower alkyl” as may be employed herein alone or as part of another group includes both straight and branched chain hydrocarbons containing 1 to 8 carbons, and the terms “alkyl” and “alk” as may be employed herein alone or as part of another group includes both straight and branched chain hydrocarbons containing 1 to 20 carbons, preferably 1 to 10 carbons, more preferably 1 to 8 carbons, in the normal chain, such as methyl, ethyl, propyl, isopropyl, butyl, t-butyl, isobutyl, pentyl, hexyl, isohexyl, heptyl, 4,4-dimethylpentyl, octyl, 2,2,4-trimethylpentyl, nonyl, decyl, undecyl, dodecyl, the various branched chain isomers thereof, and the like as well as such groups including 1 to 4 substituents such as halo, for example F, Br, Cl or I or CF₃, alkyl, alkoxy, aryl, aryloxy, aryl(aryl) or diaryl, arylalkyl, arylalkyloxy, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkylalkyl, cycloalkylalkyloxy, hydroxy, hydroxyalkyl, acyl, alkanoyl, heteroaryl, heteroaryloxy, cycloheteroalkyl, arylheteroaryl, arylalkoxycarbonyl, heteroarylalkyl, heteroarylalkoxy, aryloxyalkyl, aryloxyaryl, alkylamido, alkylamino, alkanoylamino, arylcarbonylamino, nitro, cyano, thiol, haloalkyl, trihaloalkyl and/or alkylthio.

Unless otherwise indicated, the term “cycloalkyl” as may be employed herein alone or as part of another group includes saturated or partially unsaturated (containing 1 or 2 double bonds) cyclic hydrocarbon groups containing 1 to 3 rings, any one of which may optionally be a spiro substituted cycloalkyl, including monocyclicalkyl, bicyclicalkyl and tricyclicalkyl, containing a total of 3 to 20 carbons forming the rings, preferably 3 to 10 carbons, forming the ring and which may be fused to 1 or 2 aromatic rings as described for aryl, which include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclodecyl and cyclododecyl, cyclohexenyl,

any of which groups may be optionally substituted with 1 to 4 substituents such as halogen, alkyl, alkoxy, hydroxy, aryl, aryloxy, arylalkyl, cycloalkyl, alkylamido, alkanoylamino, oxo, acyl, arylcarbonylamino, nitro, cyano, thiol and/or alkylthio and/or any of the alkyl substituents.

The term “heterocyclo”, “heterocycle”, “heterocyclyl” or “heterocyclic ring”, as may be used herein, represents an unsubstituted or substituted stable 4 to 7-membered monocyclic ring system which may be saturated or unsaturated, and which consists of carbon atoms, with one to four heteroatoms selected from nitrogen, oxygen or sulfur, and wherein the nitrogen and sulfur heteroatoms may optionally be oxidized, and the nitrogen heteroatom may optionally be quaternized. The heterocyclic ring may be attached at any heteroatom or carbon atom which results in the creation of a stable structure. Examples of such heterocyclic groups include, but is not limited to, piperidinyl, piperazinyl, oxopiperazinyl, oxopiperidinyl, oxopyrrolidinyl, oxoazepinyl, azepinyl, pyrrolyl, pyrrolidinyl, furanyl, thienyl, pyrazolyl, pyrazolidinyl, imidazolyl, imidazolinyl, imidazolidinyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, oxazolyl, oxazolidinyl, isooxazolyl, isoxazolidinyl, morpholinyl, thiazolyl, thiazolidinyl, isothiazolyl, thiadiazolyl, tetrahydropyranyl, thiamorpholinyl, thiamorpholinyl sulfoxide, thiamorpholinyl sulfone, oxadiazolyl and other heterocycles described in Katritzky, A. R. and Rees, C. W., eds. Comprehensive Heterocyclic Chemistry: The Structure, Reactions, Synthesis and Uses of Heterocvclic Compounds 1984, Pergamon Press, New York, N.Y.; and Katritzky, A. R., Rccs, C. W., Scriven, E. F., eds. Comprehensive Heterocyclic Chemistry 11: A Review of the Literature 1982-1995 1996, Elsevier Science, Inc., Tarrytown, N.Y.; and references therein.

The term “alkanoyl” as may be used herein alone or as part of another group refers to alkyl linked to a carbonyl group.

The term “halogen” or “halo” as may be used herein alone or as part of another group refers to chlorine, bromine, fluorine, and iodine, with chlorine or fluorine or bromine sometimes being preferred.

Unless otherwise indicated, the term “aryl” or “Aryl” as may be employed herein alone or as part of another group refers to monocyclic and bicyclic aromatic groups containing 6 to 10 carbons in the ring portion (such as phenyl or naphthyl including 1-naphthyl and 2-naphthyl) and may optionally include one to three additional rings fused to a carbocyclic ring or a heterocyclic ring (such as aryl, cycloalkyl, heteroaryl or cycloheteroalkyl rings). For example

and may be optionally substituted through available carbon atoms with 1, 2, or 3 groups selected from hydrogen, halo, haloalkyl, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, trifluoromethyl, trifluoromethoxy, alkynyl, cycloalkyl-alkyl, cycloheteroalkyl, cycloheteroalkylalkyl, aryl, heteroaryl, arylalkyl, aryloxy, aryloxyalkyl, arylalkoxy, alkoxycarbonyl, arylcarbonyl, arylalkenyl, aminocarbonylaryl, arylthio, arylsulfinyl, arylazo, heteroarylalkyl, heteroarylalkenyl, heteroarylheteroaryl, heteroaryloxy, hydroxy, nitro, cyano, thiol, alkylthio, arylthio, heteroarylthio, arylthioalkyl, alkoxyarylthio, alkylcarbonyl, arylcarbonyl, alkylaminocarbonyl, arylaminocarbonyl, alkoxycarbonyl, aminocarbonyl, alkylcarbonyloxy, arylcarbonyloxy, alkylcarbonylamino, arylcarbonylamino, arylsulfinyl, arylsulfinylalkyl, arylsulfonylamino and arylsulfonaminocarbonyl and/or any of the alkyl substituents set out herein.

Unless otherwise indicated, the term “heteroaryl” as may be used herein alone or as part of another group refers to a 5- or 6-membered aromatic ring which includes 1, 2, 3 or 4 hetero atoms such as nitrogen, oxygen or sulfur. Such rings may be fused to an aryl, cycloalkyl, heteroaryl or heterocyclyl and include possible N-oxides as described in Katritzky, A. R. and Rees, C. W., eds. Comprehensive Heterocyclic Chemistry: The Structure, Reactions, Synthesis and Uses of Heterocyclic Compounds 1984, Pergamon Press, New York, N.Y.; and Katritzky, A. R., Rees, C. W., Scriven, E. F., eds. Comprehensive Heterocyclic Chemistry II: A Review of the Literature 1982-1995 1996, Elsevier Science, Inc., Tarrytown, N.Y.; and references therein. Further, “heteroaryl”, as defined herein, may optionally be substituted with one or more substituents such as the substituents included above in the definition of “substituted alkyl” and “substituted aryl”. Examples of heteroaryl groups include the following:

and the like.

Unless otherwise indicated, the term “lower alkoxy”, “alkoxy”, “aryloxy” or “aralkoxy” as may be employed herein alone or as part of another group includes any of the above alkyl, aralkyl or aryl groups linked to an oxygen atom.

Unless otherwise indicated, the term “lower alkylthio”, alkylthio”, “arylthio” or “aralkylthio” as may be employed herein alone or as part of another group includes any of the above alkyl, aralkyl or aryl groups linked to a sulfur atom.

The term “polyhaloalkyl” as may be used herein refers to an “alkyl” group as defined above which includes from 2 to 9, preferably from 2 to 5, halo substituents, such as F or Cl, preferably F, such as CF₃CH₂, CF₃ or CF₃CF₂CH₂.

The term “polyhaloalkyloxy” as may be used herein refers to an “alkoxy” or “alkyloxy” group as defined above which includes from 2 to 9, preferably from 2 to 5, halo substituents, such as F or Cl, preferably F, such as CF₃CH₂O, CF₃O or CF₃CF₂CH₂O.

The terms “R_(n)” as used herein are to be construed with reference to the specific structure in which are utilized and described, and may be used more than once.

PET based radiotracers for mapping the nervous system have been developed in an attempt to address the limitations of prior radiotracers. In some embodiments of the present invention, the PET based radiotracers are developed to exhibit increased stability, decreased NE release (thereby reducing side effects), improved quantitative information, and/or high affinity for VMAT. In certain embodiments, these tracers are based on compounds that are derivatized with ¹⁸F in a variety of positions: aryl, alkyl, a keto, benzylic, beta-alkylethers, gamma-propylalkylethers and beta-proplylalkylethers, as shown in their structures below. In alternative embodiments, a methyl group a is added to the amine, and/or the catechol functionality is either eliminated or masked as a way of making these molecules more stable.

PET based radiotracers for mapping the cardiac sympathetic nerve system include General Structures I and II:

Examples of compounds represented by General Structures I & II include the following:

One embodiment of the present invention provides PET based radiotracers as illustrated in the General Structure I above, wherein m=0, 1, or 2; n=0, 1, 2, and A is O or absent. R, R₁, R₂, and R₃ are independently selected from the group consisting of H, OR₄, F, Cl, CF₃, Br, I, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₄, CO₂R₄, N(R₄)₂, CN, C(═NH)NHR₅, C(═O)NHR₅, NHC(═O)NR₅, NHNR₅, SO₂OR₅, and imaging moiety Im. Q comprises bridging groups that can be present between Y and Z, and to R₂. The Q bridging groups can independently be selected from the group consisting of CH₂, CH, CR₅, N, NH, NR₅, O and S in such a combination as to create a chemically stable structure. The substituents W, X, Y and Z may independently be selected from the group consisting of H, OR₄, NR₄, F, Cl, Br, I, Im, aryl, and heteroaryl. R₄ and R₅ may be H, alkyl, aryl or heteroaryl substituents. In an alternative embodiment, the alkyl, aryl or heteroaryl substituents may be substituted with various functional groups selected from the group consisting of, but not limited to, halogen (F, Cl, Br, I), OH, NH₂, COOH, Im, COOR₁₃, CON(R₁₃)₂, SR₁₃, OR₁₃, NHC(═NH)NH₂, NHC(═O)NH₂, NHC(═O)N(R₁₃)₂, C(═NH)NH₂, C(═NR₁₃)N(R₁₃)₂ and N(R₁₃)₂, in which R₁₃ may be hydrogen, alkyl, aryl or alkylaryl.

Another embodiment provides PET based radiotracers as illustrated in the General Structure II above, wherein linking groups B, D, E, F and G are independently selected from the group consisting of a bond, alkyl (C₁-C₅; preferably C₂), aryl, aralkyl, alkylaryl, heteroaryl, alkoxy, alkylarnino, aryloxy, alkoxyalkyl, and heterocyclic. R₆ through R₁₂ may be independently selected from the group consisting of H, OR₄, F, Cl, CF₃, Br, I, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₄, CO₂R₄, N(R₄)₂, CN, C(═NH)NHR₅, C(═O)NHR₅, NHC(═O)NR₅, NHNR₅, SO₂OR₅, and Im. R₄ and R₅ may be H, alkyl, aryl or heteroaryl substituents, and Im is an imaging moiety that may be selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, ¹³¹I, ^(99m)Tc, ¹⁵³Gd, ¹¹¹In, and ⁹⁰Y. And, provided that in the case where any one of R₆-R₁₀ equals Im, the linking group B, D, E, F or G, which attaches the imaging moiety to the phenyl ring, contains at least one atom.

Structure Alpha and Examples:

A further embodiment provides PET based radiotracers as illustrated in Structure Alpha and non-limiting Examples above, which in its simplest form may be considered a hybrid of structures I and II. In Structure Alpha n=0, 1, 2, 3 and A is O or absent. R, R₁, R₂ and R₃ are independently selected from the group consisting of H, OR₄, F, Cl, Br, I, CF₃, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₄, CO₂R₄, N(R₄)₂, CN, C(═NR₄)OR₅, NR₄(C(═NR₅)NHR₆, C(═NR₄)NHR₅, C(═O)NHR₄, NR₄C(═O)NR₅, NR₄NR₅, SO₂OR₄, and Im. The substituents W, X, Y and Z can independently be selected from the group consisting of H, OR₄, N(R₄)₂, F, Cl, Br, I, CF₃, Im, aryl, and heteroaryl. R₄, R₅, and R₆ are H, alkyl, aryl or heteroaryl substituents. In an alternative embodiment, any two of R₄, R₅, or R₆ may form a cyclic structure selected from the group consisting of —CH₂—CH₂—, —CH₂—CH₂—CH₂, —CH═CH—, —X═CH—, and —X—CH═CH—, wherein X is O, NH, N═, or NR₇, and wherein R₇ is an alkyl, aryl or heteroaryl substituent. In a further alternative embodiment, the alkyl, aryl or heteroaryl substituents of R₄-R₇ may be substituted with various functional groups selected from the group consisting of but not limited to halogen (F, Cl, Br, I), OH, NH₂, COOH, Im, COOR₈, CON(R₈)₂, SR₈, OR₈, NHC(═NH)NH₂, NHC(═O)NH₂, NHC(═O)N(R₈)₂, C(═NH)NH₂, C(═NR₈)N(R₈)₂ and N(R₈)₂, in which R₈ may be hydrogen, alkyl, aryl or alkylaryl. The imaging moiety, Im, is selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, ¹³¹I, ^(99m)Tc, 153Gd, or 11In, and can be present in either W—Z or R-R₇.

Structure Beta and Examples:

In yet a further embodiment, PET based radiotracers are described as illustrated in Structure Beta and non-limiting Examples above. In Structure Beta n=0, 1, 2, 3 and A=O or is absent. R, R₁, R₂ and R₃ are independently selected from the group consisting of H, OR₄, F, Cl, Br, I, CF₃, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₄, CO₂R₄, N(R₄)₂, CN, C(═NR₄)OR₅, NR₄(C(═NR₅)NHR₆, C(═NR₄)NHR₅, C(═O)NHR₄, NR₄C(═O)NR, NR₄NR₅, SO₂OR₄, and Im. The substituents W and X can independently be selected from the group consisting of H, OR₄, N(R₄)₂, F, Cl, Br, I, CF₃, Im, aryl, and heteroaryl. Y and Z can be selected from the group consisting of CH, CH₂, O, N, NR₇, and CH═CH. Bridging group Q is absent or selected from the group consisting of CH, CR₄, CH₂, N, NR₄, NH, S, and O. R₄, R₅, and R₆ are H, alkyl, aryl or heteroaryl substituents. In an alternative embodiment, any two of R₄, R₅, or R₆ may form a cyclic structure selected from the group consisting of —CH₂—CH₂—, —CH₂—CH₂—CH₂—, —CH═CH—, —X═CH—, and —X—CH═CH—, wherein X is O, NH, N═, or NR₇, and wherein R₇ is an alkyl, aryl or heteroaryl substituents. In a further alternative embodiment, the alkyl, aryl or heteroaryl substituents of R₄-R₇ may substituted with various functional groups selected from the group consisting of but not limited to halogen (F, Cl, Br, I), OH, NH₂, COOH, Im, COOR₈, CON(R₈)₂, SR₈, OR₈, NHC(═NH)NH₂, NHC(═O)NH₂, NHC(═O)N(R₈)₂, C(═NH)NH₂, C(═NR₈)N(R₈)₂ and N(R₈)₂, in which R₈ may be hydrogen, alkyl, aryl or alkylaryl. The imaging moiety, Im, is selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, ¹³¹I, ^(99m)Tc, ¹⁵³Gd, or ¹¹¹In, and can be present in either W—Z or R-R₇.

Structure Chi:

In an even further preferred embodiment, PET based radiotracers are described as illustrated in Structure Chi above. R through R₂ of Structure Chi are independently selected from the group consisting of H, OR₃, F, Cl, Br, I, CH₂F, OCH₂CH₂F, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₃, CO₂R₃, and Im. Im is a imaging moiety and is selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, and ¹³¹I. R₃ can be an H, alkyl, aryl or heteroaryl substituent. In an alternative embodiment the alkyl, aryl, aralkyl, alkylaryl or heteroaryl substituents of R-R₃ may be substituted with functional groups selected from the group consisting of but not limited to halogen (F, Cl, Br, I), OH, NH₂, COOH, Im, COOR₄, CON(R₄)₂, SR₄, OR₄, NHC(═NH)NH₂, NHC(═O)NH₂, NHC(═O)N(R₄)₂, C(═NH)NH₂, C(═NR₄)N(R₄)₂ and N(R₄)₂, in which R₄ may be hydrogen, alkyl, aryl or alkylaryl.

Structure Delta:

A further embodiment describes PET based radiotracers as illustrated in Structure Delta above, wherein linking groups B, D, E, F and G are independently selected from the group consisting of a bond, alkyl (C₁-C₅; preferably C₂), aryl, aralkyl, alkylaryl, heteroaryl, alkoxy, alkylamino, aryloxy, and alkoxyalkyl. R₈ through R₁₄ are independently selected from the group consisting of H, OR₃, F, Cl, Br, I, CH₂F, OCH₂CH₂F, alkyl (C₁-C₄), aryl, heteroaryl, C(═O)R₃, CO₂R₃, and Im. R₃, R₄, R₅, and R₆ can independently be selected from the group consisting of H, alkyl, aryl, aralkyl, heteroaryl, alkylamino, alkyloxy, and aryloxy. In an alternative embodiment any two of R₄, R₅, R₆, R₁₃, or R₁₄ may form a cyclic structure selected from the group consisting of a bond, —CH₂—, —CH₂—CH₂—, —CH₂—CH₂—CH₂—, —CH═CH—, —X═CH—, and —X—CH═CH—, wherein X is O, NH, N═, or NR₇, and wherein R₇ is an alkyl, aryl or heteroaryl substituent. In a further alternative embodiment, the alkyl, aryl or heteroaryl substituents of R₃-R₇ may be substituted with various functional groups selected from the group consisting of but not limited to halogen (F, Cl, Br, I), OH, NH₂, COOH, Im, COOR₁₅, CON(R₁₅)₂, SR₁₅, OR₁₅, NHC(═NH)NH₂, NHC(═O)NH₂, NHC(═O)N(R₁₅)₂, C(═NH)NH₂, C(═NR₁₅)N(R₁₅)₂ and N(R₁₅)₂, wherein R₁₅ may be hydrogen, alkyl, aryl or alkylaryl. The imaging moiety, Im, can be selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, ¹³¹I, ^(99m)Tc, ¹⁵³Gd, and ¹¹¹In, and may be present in either W—Z or R₄-R₇. And, provided that in the case where any one of R₈-R₁₂ equals Im, the linking group B, D, E, F or G, which attaches the imaging moiety to the phenyl ring, contains at least one atom.

Structure Epsilon:

A preferred embodiment describes the PET based radiotracer N-[3-bromo-4-(3-[¹⁸F]fluoropropoxy)-benzyl]-guanidine hydrochloride, as illustrated in Structure Epsilon above. Structure Epsilon may be derived from Structure Alpha, wherein R₁, R₃, X and W are hydrogen, n is zero, R is guanidine (NHC(═NH)NH₂), Y is bromine and Z is OCH₂CH₂CH₂ ¹⁸F.

Additional preferred compounds as part of the invention include the following:

A further embodiment includes a method of imaging cardiac innervation comprising the steps of: administering an effective amount of one or more of the novel compounds herein set forth above, to a patient; detecting gamma radiation emitted by said compound; and forming an image therefrom. The method utilizes PET perfusion scanning or SPECT imaging techniques available to the skilled artisan, or other methods which may be employed.

There is also provided a composition useful in medical imaging which comprises one or more of the compounds hereinabove set forth, together with one or more excipients.

The compounds hereinabove described may be synthesized by methods available to the skilled artisan, which are in part further exemplified by the non-limiting Examples below.

EXAMPLES

The following examples are provided to demonstrate and further illustrate certain preferred embodiments of the present invention and are not to be construed as limiting the scope thereof.

General Experimental.

¹H NMR spectra were recorded on a Bruker Avance DRX 600 MHz spectrometer or on a Bruker Avance 300 MHz spectrometer. Chemical shifts are reported in ppm from tetramethylsilane with the residual solvent resonance resulting from incomplete deuteration as the internal standard (CDCl₃: δ 7.25 ppm, CD₃CN: δ 1.94 ppm, DMSO-d₆: δ 2.50 ppm). Data are reported as follows: chemical shift, multiplicity (s=singlet, d=doublet, t=triplet, q=quartet, quin=quintet, b or br=broad, m=multiplet), coupling constants, and integration. ¹³C NMR spectra were recorded on a Bruker Avance DRX 150 MHz or on a Bruker Avance 75 MHz spectrometer with complete proton decoupling. Chemical shifts are reported in ppm from tetramethylsilane with the solvent as the internal reference (CDCl₃: δ 77.0 ppm, CD₃CN: δ 118.1 ppm, DMSO-d₆: δ 39.5 ppm). ¹⁹F NMR spectra were recorded on a Bruker Avance DRX 565 MHz spectrometer. Chemical shifts are reported in ppm relative to an external standard (CCl₃F; δ=0.00 ppm). Low-resolution mass spectrometry was performed on an Agilent Technologies 1100 Series LC/MS EST-MS (positive mode). High-resolution mass spectrometry was performed on an Ionspec Ultima FTMS; ESI-MS (positive mode), or on an Agilent MSD-TOF; ESI-MS (positive mode). Melting points were determined using a Thomas-Hoover melting point apparatus and are uncorrected.

Unless otherwise stated, all reactions were conducted under an inert atmosphere of dry nitrogen. Indicated temperatures refer to those of the reaction bath, while ambient laboratory temperature is noted as 22° C. Anhydrous dimethylformamide (DMF), dimethylsulfoxide (DMSO), acetonitrile (McCN), pyridine, triethylamine (TEA), and diisopropylethylamine (DIEA) were obtained from Aldrich in SureSeal® bottles. Absolute ethanol was obtained from Quantum Chemical Corp. Merck silica gel, grade 9385, 230-400 mesh, 60 Å was used for flash chromatography. Ethyl acetate (EtOAc), chloroform (CHCl₃), methanol (MeOH), HPLC grade acetonitrile (MeCN), dichloromethane (DCM), ethyl ether, acetone, sodium hydroxide (NaOH), and hydrochloric acid (HCl) were obtained from Baker. 1-Trityl-1H-imidazole-2-amine was prepared according to a published procedure (U.S. Pat. No. 6,130,231, incorporated by reference in its entirety). 1-Bromo-2-fluoroethane was purchased from Alfa Aesar. 3-Methoxy-4-fluorobenzonitrile was purchased from TCI. MDCK cell membranes expressing human norepinephrine transporter, and [³H]desipramine were purchased from Perkin-Elmer. [¹⁸F]NaF was obtained from PETNET Pharmaceutical Services (Cummings Park, Woburn, Mass.) on a MP1 anion exchange resin (BioRad) cartridge. Other reagents were obtained from Lancaster Synthesis, Inc., Sigma-Aldrich Chemical Co, or Fluka Chemical Corp.

Example 1 Synthesis of N-(4-Fluoro-3-(trifluoromethyl)benzyl)-1H-imidazol-2-amine

Part A—Preparation of N-(4-Fluoro-3-(trifluoromethyl)benzyl)-1-trityl-1H-imidazol-2-amine

A solution of 4-fluoro-3-(trifluoromethyl)benzaldehyde (227 mg, 1.18 mmol) and 1-trityl-1H-imidazole-2-amine (462.3 mg, 1.42 mmol) in toluene (40 mL) was heated at reflux for 6 h while using a Dean-Stark apparatus to remove water. The mixture was cooled to room temperature, treated with sodium triacetoxyborohydride (1.00 g, 4.70 mmol), and stirred overnight. The reaction was quenched by the addition of water (150 mL), and the layers were separated. The aqueous layer was extracted with ethyl acetate (2×50 mL). The combined organic layers were dried (MgSO₄) and concentrated, and the resulting residue was purified by flash chromatography (40:60 EtOAc/hexanes) to yield the title compound as a pale yellow solid (266 mg, 45%). ¹H NMR (CDCl₃, 300 MHz): δ 7.38-7.30 (m, 9H), 7.24-7.14 (m, 6H), 7.14-6.93 (m, 3H), 6.71 (d, J=3.0 Hz, 1H), 6.45 (d, J=3.0 Hz, 1H), 4.28 (d, J=6.0 Hz, 2H), 3.26 (t, J=6.0 Hz, 1H); ¹³C NMR (CDCl₃, 75 MHz): δ 158.69 (d, J=253.5), 149.54, 141.52, 135.56, 132.82 (d, J=8.2 Hz), 129.93, 128.16, 128.07, 125.86, 122.44, 118.19-117.60 (m), 117.30, 116.48 (d, J=20.25 Hz), 73.91, 46.54. MS (ESI): 243.2 (Trt carbocation, 100).

Part B—Preparation of N-(4-Fluoro-3-(trifluoromethyl)benzyl)-1H-imidazol-2-amine

A solution of the product of Part A (150 mg, 0.30 mmol) in 5:95 triisopropylsilane/TFA (2.0 mL) was heated at 60° C. for 2 h, and concentrated. The residue was dissolved in DCM (20 mL) and washed with 5% Na₂CO₃ (10 mL). The organic layer was dried (Na₂SO₄) and concentrated. The resulting crude product was purified by flash chromatography (MeOH/DCM, 10/90-15/85) to yield the title compound as a light gray oil (49.7 mg, 64%). ¹H NMR (CDCl₃, 600 MHz): δ 7.51 (d, J=6.0 Hz, 1H), 7.50-7.46 (m, 1H), 7.10 (t, J=9.6 Hz, 1H), 6.57 (s, 2H), 5.31 (bs, 3H), 4.41 (s, 2H); ¹³C NMR (CDCl₃, 150 MHz): δ 159.21 (d, J=254.4), 149.86, 135.27, 132.82 (d, J=8.2 Hz), 126.04 (d, J=3.9 Hz), 122.69 (q, J=270.8 Hz), 119.02-118.36 (m), 117.55, 117.35 (d, J=20.7 Hz), 46.99; ¹⁹F NMR (CDCl₃, 565 MHz): δ −61.39 (d, J=12.4 Hz), −116.39 (t, J=6.2 Hz). MS (ESI): 260.2 (M+H, 100); HRMS calc'd for C₁₁H₁₀F₄N₃(M+H): 260.0805; Found: 260.0807.

Example 2 Synthesis of 1-(2-(4-(2-fluoroethoxy)phenyl)-2-hydroxyethyl)guanidinium Chloride

Part A—Preparation of 1-(2-Hydroxy-2-(4-hydroxyphenyl)ethyl)-2,3-bis(tert-butoxycarbonyl)guanidine

A solution of (+/−)-octopamine hydrochloride (500 mg, 2.89 mmol) and N,N′-bis(Boc)-1H-pyrazole-1-carboxamidine (1.13 g, 3.60 mmol) in DMF (10 mL) was stirred for 1 h at ambient temperatures. The reaction mixture was concentrated, and the residue was dissolved in EtOAc (60 mL). The solution was washed with 1N KHSO₄ (2×30 mL) and 5% Na₂CO₃ (30 mL). The organic layer was dried (Na₂SO₄), concentrated, and purified by flash chromatography (EtOAc/hexane 30/70-50/50) to yield the title compound as a colorless solid (836 mg, 73%). ¹H NMR (CDCl₃, 600 MHz): δ 11.45 (bs, 1H), 8.76 (s, 1H), 7.15 (d, J=8.4 Hz, 2H), 6.77 (d, J=8.4 Hz, 2H), 6.52 (bs, 1H), 4.81-4.78 (m, 1H), 3.66-3.50 (m, 2H), 1.51 (s, 9H), 1.49 (s, 9H); ³C NMR (CDCl₃, 150 MHz): δ 162.86, 157.52, 156.04, 153.19, 133.52, 127.34, 115.65, 83.83, 80.07, 73.95, 49.49, 28.41, 28.26. MS (ESI): 396.4 (M+H, 100), 340.3 (M+H−tBu, 15).

Part B—Preparation 1-(2-(4-(2-Fluoroethoxy)phenyl)-2-hydroxyethyl)-2,3-bis(tert-butoxycarbonyl) guanidine

A mixture of the product of Part A (311 mg, 0.79 mmol), K₂CO₃ (163 mg, 1.18 mmol), KI (1.2 mg, 0.0070 mmol), and 2-bromofluoroethane (59 μL, 0.79 mmol) in DMSO (2.0 mL) was stirred at 50° C. for 3 h, followed by room temperature overnight. Water (15 mL) was added and the mixture was extracted with EtOAc (2×15 mL). The combined organic layers were washed with saturated NaCl (10 mL), dried (Na₂SO₄) and concentrated. The crude residue was purified with flash chromatography (EtOAc/hexane) to yield the title compound as a colorless solid (177 mg, 51%). ¹H NMR (DMSO-d₆, 300 MHz): δ 11.47 (s, 1H), 8.70 (s, 1H), 7.35-7.31 (m, 2H), 6.95-6.89 (m, 2H), 4.85-4.82 (m, 2H), 4.69-4.66 (m, 1H), 4.28-4.25 (m, 1H), 4.19-4.16 (m, 1H), 3.68-3.61 (m, 2H), 1.51 (s, 18H); ¹³C NMR (DMSO-d₆, 75 MHz): δ 162.91, 158.21, 157.73, 153.21, 135.18, 127.42, 114.85, 83.81, 82.13 (d, J=169.5 Hz), 79.96, 74.26, 67.42 (d, J=20.2 Hz), 49.82, 28.44, 28.25. MS (ESI): 464.1 (M+Na, 6), 442.1 (M+H, 100), 386.1 (M+H−tBu, 8).

Part C—Preparation of 1-(2-(4-(2-Fluoroethoxy)phenyl)-2-hydroxyethyl)guanidinium Chloride

The product of Part B (15.0 mg, 0.034 mmol) was dissolved in a solution of dioxane (1.0 mL) and 37% aqueous HCl (4.0 mL), and allowed to stand at ambient temperature for 40 min. The mixture was concentrated and the resulting residue was purified by HPLC using a Phenomenex Luna C18(2) column (250×21.2 mm, 10μ, 100 Å) using a 0.72%/min gradient of 0-18% ACN containing 0.1% formic acid at a flow rate of 20 mL/min. Pure fractions were lyophilized to give a hygroscopic formate salt. This material was re-lyophilized from 0.5N HCl to give the title compound as a dry colorless solid (4.5 mg, 48%). ¹H NMR (1:1 CD₃CN/D₂O, 600 MHz): δ 7.31-7.27 (m, 2H), 6.95-6.92 (m, 2H), 4.74-4.73 (m, 2H), 4.69-4.66 (m, 1H), 4.25-4.17 (m, 2H), 3.34-3.28 (m, 2H); ¹³C NMR (1:1 CD₃CN/D₂O, 150 MHz): δ 159.01, 158.42, 134.89, 128.56, 115.70, 83.62 (d, J=164.4 Hz), 72.24, 68.44 (d, J=18.9 Hz), 49.31. MS (ESI): 224.3 (M+H−H₂O, 100); HRMS calc'd for C₁₁H₁₇FN₃O₂ (M+H): 242.1299; Found: 242.1297.

Example 3 Synthesis of 1-(4-(2-Fluoroethoxy)phenethyl)guanidinium Chloride

The product of Example 2, Part B (88.4 mg, 0.20 mmol) was dissolved in a solution of TFA (1.9 mL), triisopropylsilane (0.05 mL), and water (0.05 mL). The reaction solution was heated at 55° C. for 10 min and concentrated. The crude mixture was purified by HPLC using the procedure of Example 2, Part B. The product fraction was lyophilized yielding a hygroscopic solid.

Relyophilization from 0.5N HCl gave the title compound as a dry colorless solid (12.4 mg, 24%). ¹H NMR (1:1 CD₃CN/D₂O, 600 MHz): δ 7.18-7.14 (m, 2H), 6.90-6.87 (m, 2H), 4.75-4.65 (m, 2H), 4.22-4.15 (m, 2H), 3.31 (t, J=7.2 Hz, 2H), 2.76 (t, J=7.2 Hz, 2H); ¹³C NMR (1:1 CD₃CN/D₂O, 150 MHz): δ 158.08, 157.75, 132.00, 131.09, 115.82, 83.65 (d, J=164.6 Hz), 68.44 (d, J=18.8 Hz), 43.57, 34.36. HRMS calculated for C₁₁H₁₇FN₃O (M+H): 226.1350; Found: 226.1352.

Example 4 Synthesis of 4-(4-(2-Fluoroethoxy)phenyl)imidazolidin-2-iminium Chloride

Synthesis of the product of Example 3 also yielded the title compound as a colorless solid (14.2 mg, 27%). ¹H NMR (1:1 CD₃CN/D₂O, 600 MHz): δ 7.29-7.26 (m, 2H), 6.98-6.94 (m, 2H), 5.03 (dd, J=7.8, 9.6 Hz, 1H), 4.78-4.66 (m, 2H), 4.26-4.18 (m, 2H), 4.00 (t, J=9.6 Hz, 1H), 3.41 (dd, J=7.2, 9.6 Hz, 1H); ¹³C NMR (1:1 CD₃CN/D₂O, 150 MHz): δ 160.52, 159.38, 133.73, 128.78, 116.04, 83.59 (d, J=164.7 Hz), 68.47 (d, J=18.8 Hz), 58.84, 52.07. HRMS calc'd for C₁₁H₁₅FN₃O (M+H): 224.1194; Found: 224.1197.

Example 5 Synthesis of (E)-1-(4-(2-Fluoroethoxy)styryl)guanidinium Chloride

Synthesis of the product of Example 3 also yielded the title compound as a colorless solid (1.2 mg, 2.5%). ¹H NMR (1:1 CD₃CN/D₂O, 600 MHz): δ 7.34-7.28 (m, 2H), 6.93-6.87 (m, 3H), 6.23 (d, J=14.4 Hz, 1H), 4.76-4.65 (m, 2H), 4.24-4.15 (m, 2H); ¹³C NMR (1:1 CD₃CN/D₂O, 150 MHz): δ 158.70, 155.21, 129.52, 128.20, 120.92, 117.08, 116.04, 83.58 (d, J=164.4 Hz), 68.46 (d, J=18.9 Hz). MS (ESI): 224.3 (M+H, 100).

Example 6 Synthesis of 5-(2-Amino-1-hydroxypropyl)-2-(2-fluoroethoxy)benzene-1,3-diol Hydrochloride

Part A—Preparation of Methyl 4-(2-Fluoroethoxy)3,5-dihydroxybenzoate

To a 100 mL round bottom flask was added methyl 3,4,5-trihydroxybenzoate (7.00 g, 88.0 mmol) followed by 25 mL of dimethyl sulfoxide. Potassium Carbonate (7.88 g, 57.0 mmol), potassium iodide (31.6 mg, 0.19 mmol) and 1-bromo-2-fluoroethane (5.79 g, 45.6 mmol) were successively added followed by 25 mL more of dimethyl sulfoxide. The reaction mixture was stirred for 18 h after which it was diluted by adding water (100 mL). The mixture was poured into a separatory funnel and extracted with DCM (3×40 mL). The organic layer was then washed with water (4×120 mL) and brine, and dried over magnesium sulfate. The organic layer was then concentrated to obtain an oil. The crude oil was purified using silica gel flash chromatography (DCM/ether 39:1) to obtain 1.9 g (22%) of the title compound (R_(f)˜0.17 in 19:1 DCM/ether). ¹H NMR (600 MHz, CDCl₃): δ 7.25 (s, 2H), 5.96 (s, 2H), 4.7 (t of d, 2H, J=48, 1.2 Hz), 4.37 (t of d, 2H, J=24, 1.2 Hz), 3.87 (s, 3H). ¹³C NMR (150 MHz, CDCl₃): δ 166.8, 149, 136.8, 126.4, 109.8, 82.16 (d, J=334 Hz), 72.6 (d, J=37.5), 52.3. MS (ESI): 231.4 (M+H, 100); HRMS: Calc'd for C₁₀H₁₁FO₅ (M+H): 231.06633; Found: 231.0664.

Part B—Preparation of Methyl 4-(2-Fluoroethoxy) 3,5-bis(methoxymethyloxy)benzoate

A flame dried 100 ml round bottom flask fitted with a reflux condenser was charged with sodium iodide (3.00 g, 20 mmol) and to this was added 1,2-dimethoxyethane (20 mL). Methoxymethyl chloride (2.09 g, 1.97 mL, 26.0 mmol) was then added drop-wise to this mixture. A colorless precipitate formed. This mixture was stirred for 5 min after which the product of Part A (1.5 g, 6.51 mmol) dissolved in dimethoxyethane (20 mL) was added to it. Diisopropylethylamine (3.36 g, 4.53 mL, 26.04 mmol) was added to the above mixture and the flask was immersed in an oil bath at 80° C. The resulting mixture was stirred at this temperature for 15 h after which it was cooled to room temperature. Water (20 mL) was added and the mixture was extracted with dichloromethane (2×40 mL). The combined organic layers were then washed with brine and dried over magnesium sulfate. Concentration of the organic layer in vacuo gave a pale red oil which was subjected to silica gel flash chromatography (hexanes/ether 4:1 to 7:3) to obtain 0.9 g (44%) of the product as a viscous oil. ¹H NMR (600 MHz, CDCl₃): δ 7.5 (s, 2H), 5.25 (s, 4H), 4.7 (t of d, 2H, J=49, 1.2 Hz), 4.3 (d of t, 2H, J=24, 1.2 Hz), 3.88 (s, 3H), 3.5 (s, 6H). ¹³C NMR (150 MHz, CDCl₃): δ 166.3, 150.6, 142.9, 125.8, 112.1, 95.4, 82.61 (d, J=339 Hz), 72.3 (d, J=40.5 Hz), 56.4, 52.2. HRMS: Calc'd for C₁₄H₁₉FO₇ (M+H): 319.1187; Found: 319.1185.

Part C—Preparation of 4-(2-Fluoroethoxy)-3,5-bis(methoxymethyloxy)-benzaldehyde

To a flame dried 50 ml round bottom flask was added a solution of Red-Al (3.29 mL; 65 wt % solution in toluene). Toluene (10 mL) was added to the flask and the solution was cooled to 0° C. in an ice bath. Morpholine (1.01 g, 1.01 mL, 11.6 mmol) was added drop-wise to keep the gas evolution under control. After completion of addition the mixture was stirred until gas evolution ceased (˜15-20 min). This solution was added to a solution of the product of Part B (0.6 g, 1.88 mmol) in toluene (20 mL) at −50° C. via a cannula. A precipitate formed in the flask. The mixture was allowed to warm to −30° C. and stirred at this temperature for 3 h. Water (15 mL) was added drop-wise to the flask to quench the reaction and the solution was extracted with ether (2×30 mL). The organic layer was washed with brine and dried over magnesium sulfate. Concentration in vacuo gave a crude oil which was purified by silica gel flash chromatography (hexanes/ether 3:2 to 1:1) to obtain 420 mg (77%) of the title compound as an oil. ¹H NMR (600 MHz, CDCl₃): δ 9.8 (s, 1H), 7.37 (s, 1H), 5.24 (s, 4H), 4.7 (t of d, 2H, J=49, 1.2 Hz), 4.3 (d of t, 2H, J=24, 1.2 Hz), 3.51 (s, 6H). ¹³C NMR (150 MHz, CDCl₃): δ 190.7, 151.4, 144.2, 132.3, 111.9, 104.2, 95.5, 82.61 (d, J=169 Hz), 72.3 (d, J=20.1 Hz), 56.4. HRMS: Calculated for C₁₃H₁₇FO₆ (M+H): 218.1081; Found: 289.1082.

Part D—Preparation of 1-(4-(2-Fluoroethoxy)-3,5-bis(methoxymethoxy)-phenyl)-2-nitropropan-1-ol

A flame dried 15 mL round bottom flask was charged with product from Part C (270 mg, 0.93 mmol) and to this was added nitroethane (5 mL) and the solution was cooled to 0° C. Tetramethylguanidine (4 drops as measured by a Pasteur pipette) was added to the above mixture and the contents were stirred for 90 min. The mixture was poured into a separatory funnel containing water (5 mL) and extracted with ethyl acetate (2×15 mL). The organic layer was washed with brine and dried over magnesium sulfate. Concentration in vacuo gave a crude oil which was purified by silica gel flash chromatography (hexanes/ether 3:2) to obtain 130 mg (18%) of the title compound as an oil in a 3:1 (A:B) mixture of diastereomers. The OH proton in pair B and both the CHNO₂ protons in pair A were heavily overlaid with other signals causing ambiguity and are hence not reported. Pair A: ¹H NMR (600 MHz, CDCl₃): δ 6.85 (s, 2H), 5.2 (s, 4H), 4.92 (d of d, 1H, J=4.2, 9 Hz), 4.7 (d of t, 2H, J=49, 1.2 Hz), 4.25 (d of t, 2H, J=24, 1.2 Hz), 3.5 (s, 6H), 2.5 (d, 1H, J=4.2 Hz), 1.35 (d, 3H, J=6.6 Hz). ¹³C NMR (150 MHz, CDCl₃): δ 151.4, 139.4, 134.3, 109.6, 95.6, 88.2, 82.64 (d, J=169 Hz), 76, 73.5, 72.3 (d, J=21 Hz), 56.3, 15.3. Pair B: ¹H NMR (600 MHz, CDCl₃): δ 6.85 (s, 4H), 5.2 (s, 8H), 4.7 (d of t, 2H, J=49, 1.2 Hz), 4.25 (d of t, 2H, J=24, 1.2 Hz), 3.5 (s, 6H), 2.6 (d, 1H, J=3.6 Hz), 1.5 (d, 3H, J=7.2 Hz). ¹³C NMR (150 MHz, CDCl₃): δ 151.2, 138.9, 134.6, 108.8, 95.6, 87.2, 82.64 (d, J=169 Hz), 76, 73.5, 72.3 (d, J=21 Hz), 56.3, 12.2. HRMS: Calc'd for C₁₅H₂₂FNO₈ (M+Na): 386.1221; Found: 386.1220.

Part E—Preparation of 1-(4-(2-Fluoroethoxy)-3,5-bis(methoxymethoxy)phenyl)-1-hydroxypropan-2-aminium Trifluoroacetate

The product of Part D (53 mg, 0.145 mmol) was charged to a flame dried 10 mL flask followed by methanol (1 mL). The flask was evacuated twice followed by purging with nitrogen. Pd—C(10 mg, 10 wt %) was added in one lot and the flask fitted with a hydrogen balloon. After stirring for one hour, ammonium formate (91 mg, 1.45 mmol) was added to the reaction followed by methanol (1 mL). The mixture was heated to reflux for 1 h and cooled to room temperature. The reaction mixture was filtered through a pad of Celite® and concentrated in vacuo to obtain a colorless solid. This crude solid was dissolved in water and subjected to preparative HPLC purification (Phenomenex Luna C18(2) column 10μ, 21.2×250 mm; gradient: 0-90% B over 30 min at 20 mL/min; Mobile phase A=0.1% TFA in water and B=0.1% TFA in 90% water) to obtain 10 mg (20%) of the title compound as a thick oil and as a diastereomeric mixture indistinguishable by NMR. ¹H NMR (600 MHz, CD₃OD): δ 6.9 (s, 2H), 5.2 (s, 4H), 4.7 (d of t, 2H, J=49, 1.2 Hz), 4.25 (d of t, 2H, J=24, 1.2 Hz), 3.5 (s, 6H), 3.35 (m, 1H), 1.0 (d, 3H, J=6.6 Hz). ¹³C NMR (150 MHz, CD₃OD): δ 152.5, 140.6, 138.2, 110.8, 96.9, 84.1 (d, J=167 Hz), 76, 73.8 (d, J=21 Hz), 56.8, 54.6, 15.8. HRMS: Calc'd for C₁₅H₂₄FNO₆ (M+H): 334.1660; Found: 336.1662.

Part F—Preparation of 5-(2-Amino-1-hydroxypropyl)-2-(2-fluoroethoxy)-benzene-1,3-diol Hydrochloride

To a flame dried 5 mL flask was added product of Part E (6 mg, 0.018 mmol) followed by methanol (1 mL). To this solution was added 2-3 drops of concentrated HCl and the solution was heated to reflux for 30 min. All solvent was removed in vacuo to obtain 3 mg (68%) of the title compound as a thick oil and as a mixture of diastereomers indistinguishable by NMR. ¹H NMR (600 MHz, CD₃OD): δ 6.49 (s, 2H), 4.7 (d of t, 2H, J=49, 1.2 Hz), 4.31 (d, 1H, J=8.4 Hz), 4.25 (d of t, 2H, J=24, 1.2 Hz), 3.45 (m, 1H), 1.5 (m, 3H). HRMS: Calc'd for C₁₁H₁₆FNO₄ (M+H): 246.1136; Found: 246.1134.

Example 7 Synthesis of 3-Methoxy-4-fluorobenzylguanidinium Chloride

Part A—Preparation of 3-Methoxy-4-fluorobenzylamine

A flame dried 50 mL round bottom flask was charged with lithium aluminum hydride (0.63 g, 16.6 mmol) and to this was added tetrahydrofuran (25 mL). The solution was cooled to 0° C. and 3-methoxy-4-fluorobenzonitrile (1.0 g, 6.62 mmol) was added in one portion. The ice bath was removed after an hour and the resulting mixture was stirred for 16 h after which it was cooled to 0° C. and quenched by adding 0.63 mL water, 0.63 mL 15% NaOH and 1.89 mL water drop-wise and in succession. The mixture was stirred for 20 min and filtered. The filtrate was concentrated in vacuo to obtain 890 mg (86%) of the title compound as an oil. NMR indicated no further purification was required. ¹H NMR (300 MHz, DMSO-d₆): δ 7.1 (m, 2H), 6.85 (m, 1H), 3.84 (s, 3H), 3.7 (s, 2H). ¹³C NMR (75 MHz, DMSO-d₆): δ 150.0 (d, J=240 Hz), 146.6 (d, J=10.5 Hz), 141.1 (d, J=3.75 Hz), 118.75 (d, J=6.75 Hz), 115.1 (d, J=18 Hz), 112.5, 55.75, 45.2. HRMS: Calc'd for C₈H₁₀FNO (M+H): 156.0819; Found: 156.0818.

Part B—Preparation of 3-Methoxy-4-fluorobenzyl-bis(tert-butoxycarbonyl)-guanidine

To a 10 mL flame dried flask was added the product of Part A (0.1 g, 0.644 mmol) and this was dissolved in MeCN. N,N-bis(tert-butoxycarbonyl)-1H-pyrazole-1-carboxamidine (0.2 g, 0.64 mmol) was added to the above solution and this was stirred for 30 min after which it was concentrated in vacuo to obtain a oil. This oil was purified by silica gel flash chromatography (dichloromethane) to obtain 0.22 g (86%) of the title compound as a colorless solid. ¹H NMR (600 MHz, DMSO-d₆): δ 11.46 (s, 1H), 8.65 (t, 1H, J=5.4 Hz), 7.22 (d of d, 1H, J=8.4, 2.4 Hz), 7.15 (d of t, 1H, J=8.4, 3 Hz), 6.85 (m, 1H), 4.45 (d, 2H, J=6 Hz), 3.82 (s, 3H), 1.47 (s, 9H), 1.38 (s, 9H). ¹³C NMR (150 MHz, DMSO-d₆): δ 162.8, 155.1, 151.8, 149.8, 146.7 (d, J=10.6 Hz), 134.9, 119.5, 115.4 (d, J=18 Hz), 113.7, 82.8, 78.1, 55.7, 43.1, 27.8, 27.5. HRMS: Calc'd for C₁₉H₂₈FN₃O₅(M+H): 398.2085; Found: 398.2084.

Part C—Preparation of Preparation of 3-Methoxy-4-fluorobenzylguanidinium Chloride

The product of Part B (0.06 g, 0.151 mmol) was charged to a 5 mL flame dried flask and to this was added dioxane (2 mL). Concentrated hydrochloric acid (0.5 mL) was added to the mixture and the solution was stirred at room temperature for 24 h. The reaction mixture was concentrated in vacuo, redissolved in 2 mL MeCN/water (1:1) mixture and lyophilized to obtain 35 mg (100%) of the product as the hydrochloride salt. ¹H NMR (300 MHz, DMSO-d₆): δ 8.26 (t, 1H, J=6 Hz), 7.2 (m, 2H), 6.88 (m, 1H), 4.34 (d, 2H, J=6.6 Hz), 3.84 (s, 3H). ¹³C NMR (75 MHz, DMSO-d₆): δ 157, 152.4, 149.1, 147 (d, J=10.5 Hz), 133.9, 119.4 (d, J=6.75 Hz), 115.7 (d, J=18 Hz), 113.2, 55.9, 43.5. HRMS: Calc'd for C₉H1₂FN₃O (M+H): 198.1037; Found: 198.1037.

Example 8 Synthesis of 3-Bromo-4-(2-fluoroethoxy)benzylguanidinium Chloride

Part A—Preparation of 3-Bromo-4-(2-fluoroethoxy)benzonitrile

To a flame dried 50 mL round bottom flask was added 3-bromo-4-hydroxybenzonitrile (1.0 g, 5.05 mmol) followed by 5 mL of dimethyl sulfoxide. Potassium iodide (4.2 mg, 0.025 mmol) and potassium carbonate (1.05 g, 7.58 mmol) were added. The flask was immersed in an oil bath at 85° C. and 1-bromo-2-fluoroethane (0.769 g, 0.45 mL, 6.06 mmol) was added. The reaction was stirred at this temperature for 1 h after which it was cooled to room temperature and diluted with water (10 mL). The resulting solution was extracted with dichloromethane (2×20 mL). The organic layer was then washed with water (3×20 mL) and brine, and dried over magnesium sulfate. The solution was filtered and concentrated in vacuo to obtain an oil which was purified by silica gel flash chromatography using dichloromethane. Product (1.13 g, 92%) was obtained as a colorless solid. ¹H NMR (600 MHz, CDCl₃): δ 7.83 (s, 1H), 7.57 (d of d, 1H, J=8.4, 1.8 Hz), 6.94 (d, 1H, J=8.4 Hz), 4.8 (t of d, 2H, J=49, 1.2 Hz), 4.35 (t of d, 2H, J=24, 1.2 Hz). 13C NMR (150 MHz, CDCl₃): δ 158.5, 136.9, 132.9, 117.5, 113, 106, 81.5 (d, J=171 Hz), 68.5 (d, J=21 Hz). HRMS: Calc'd for C₉H₇BrFNO (M+H): 243.9767; Found: 243.9767.

Part B—Preparation of 3-Bromo-4-(2-fluorethoxy)benzylammonium Formate

NiCl₂.6H₂O (180 mg, 0.758 mmol) was dried in a vacuum oven at 150° C. for 16 h to make anhydrous NiCl₂. This dried NiCl₂ was then charged to a flame-dried 15 mL two necked round bottom flask fitted with a reflux condenser. Anhydrous ethanol (2 mL) was added to the flask followed by the product from Part A (184 mg, 0.758 mmol) followed by sodium borohydride (86 mg, 2.27 mmol). Gas evolution was seen when sodium borohydride was added. After 90 min additional sodium borohydride (43 mg, 1.14 mmol) was added and the reaction mixture was stirred for an additional 10 min. The reaction mixture was filtered through a 0.2μ syringe filter, diluted with water (2.0 mL) and extracted with ethyl acetate (3×8 mL). The combined organic layers were washed with brine and dried over magnesium sulfate. The crude product obtained after concentration of the organic layer in vacuo was subjected to purification via preparative HPLC ((Phenomenex Luna C18(2) column 10μ, 21.2×250 mm; Mobile phase A=0.1% Formic acid in water and B=0.1% formic acid in 90% water at 20 mL/min) to obtain 38 mg (20%) of the product as the formate salt. ¹H NMR (600 MHz, DMSO-d₆): δ 8.4 (s, 2H), 7.6 (s, 1H), 7.3 (m, 1H), 7.1 (m, 1H), 4.8 (d of t, 2H, J=48, 1.2 Hz), 4.3 (d of t, 2H, J=24, 1.2 Hz), 3.7 (m, 2H). HRMS: Calc'd for C₉H₉BrFO (M+H−NH₃): 230.9820; Found: 230.9821.

Part C—Preparation of 3-Bromo-4-(2-fluoroethoxy)benzyl-bis(tert-butoxycarbonyl)guanidine

To a flame dried 10 mL round bottom flask was charged the product of Part B (30 mg, 0.102 mmol) and this was dissolved in MeCN (1.5 mL). Diisopropylethylamine (26.4 mg, 0.204 mmol) was then added to it followed by N, N-bis(tert-butoxycarbonyl)-1H-pyrazole-1-carboxamidine (31.7 mg, 0.102 mmol). The reaction mixture was stirred for 1 h after which it was concentrated and purified by silica gel flash chromatography using dichloromethane as eluant. The product (29 mg, 58%) was obtained as a sticky solid. ¹H NMR (600 MHz, DMSO-d₆): δ 11.4 (s, 1H), 8.65 (t, 1H, J=6, 5.4 Hz), 7.58 (s, 1H), 7.28 (d of d, 1H, J=8.4, 1.8 Hz), 7.1 (d, 1H), 4.75 (d of t, 2H, J=48, 5.4, 1.2 Hz), 4.45 (d, 2H, J=6 Hz), 4.3 (d of t, 2H, J=24, 1.2 Hz), 1.47 (s, 9H), 1.39 (s, 9H). ¹³C NMR (150 MHz, CDCl₃): δ 162.8, 155.1, 153.5, 151.1, 132.3, 128.1, 113.9, 110.7, 82.8, 81.88 (d, J=166 Hz), 78.1, 68.25 (d, J=3.9 Hz), 42.3, 27.8, 27.5. HRMS: Calc'd for C₂₀H₂₉BrFN₃O₅(M+H): 490.1347; Found: 490.1349.

Part D—Preparation of 3-Bromo-4-(2-fluoroethoxy)benzylguanidinium Chloride

The product of Part C (23 mg, 0.046 mmol) was charged to a flame dried 10 mL round bottom flask and dissolved in dioxane (1.0 mL). Concentrated hydrochloric acid (1.0 mL) was added and the reaction was stirred for 16 h at ambient temperature. The reaction mixture was concentrated in vacuo, redissolved in 2 mL of MeCN/water (1:1), and lyophilized to obtain 15 mg (88%) of the product as the hydrochloride salt. ¹H NMR (600 MHz, DMSO-d₆): δ 8.12 (t, 1H, J=6 Hz), 7.56 (d, 1H, J=2.4 Hz), 7.29 (d of d, 1H, J=8.7, 2.4 Hz), 7.15 (d, 1H, J=8.4 Hz), 4.75 (t of d, 2H, J=47.4, 4.2 Hz), 4.32 (t of d, J=30, 3.6 Hz), 4.31 (d, 2H, J=6.6 Hz). ¹³C NMR (150 MHz, CDCl₃): δ 158.8, 153.7, 131.9, 131.3, 127.9, 113.9, 110.9, 81.8 (d, J=166 Hz), 68.3 (d, J=18.9 Hz), 42.6. HRMS: Calc'd for C₁₀H₁₃BrFN₃O (M+H): 290.0298; Found: 290.0298.

Example 9 Synthesis of 3-(2-Fluoroethoxy)benzylguanidinium Trifluoroacetate

Part A—Preparation of 3-(2-Fluoroethoxy)benzonitrile

To a flame dried 50 mL round bottom flask was added 3-cyanophenol (1.0 g, 8.39 mmol) followed by 10 mL dimethyl sulfoxide. Potassium iodide (7.0 mg, 0.042 mmol) and potassium carbonate (1.74 g, 12.6 mmol) were added. The flask was immersed in an oil bath at 85° C. and 1-bromo-2-fluoroethane (1.17 g, 0.686 mL, 9.23 mmol) was added. The reaction was stirred at this temperature for 30 min, cooled to room temperature, filtered, and the filtrate was diluted with water (100 mL). The resulting solution was extracted with dichloromethane (3×30 mL). The organic layer was then washed with water (5×20 mL) and brine, and dried over magnesium sulfate. The solution was filtered and concentrated in vacuo to obtain 1.31 g (94%) of an oil as the product. ¹H NMR (600 MHz, CDCl₃): δ 7.37 (m, 1H), 7.26 (m, 1H), 7.15 (m, 2H), 4.75 (t of d, 2H, J=4.2, 46.8 Hz), 4.22 (t of d, 2H, J=4.2, 27.6 Hz). ¹³C NMR (75 MHz, CDCl₃): δ 158.4, 130.4, 125, 119.8, 117.9, 117.5, 113.3, 81 (d, J=171 Hz), 67.4 (d, J=10.1 Hz).

Part B—Preparation of 3-(2-Fluoroethoxy)benzylamine

Lithium aluminum hydride (0.67 g, 17.9 mmol) was charged to a flame dried 50 mL round bottom flask and the flask was cooled to 0° C. Tetrahydrofuran (14 mL) was added to the flask, followed by the product of Part A (1.18 g, 7.14 mmol). The ice bath was removed and the mixture stirred for 1.5 h, cooled to 0° C., and quenched by adding water (0.68 mL) and 15% NaOH (0.68 mL), followed by an addition of water (2.04 mL). This mixture was stirred for 20 min, filtered, and the filtrate was concentrated to afford 1.22 g (100%) of the product as an oil. This oil was pure by NMR. ¹H NMR (300 MHz, CDCl₃): δ 7.25 (m, 1H), 6.9 (m, 2H), 6.8 (m, 1H), 4.75 (t of d, 2H, J=4.2, 47 Hz), 4.25 (t of d, 2H, J=4.2, 28 Hz), 3.8 (s, 2H). ¹³C NMR (75 MHz, CDCl₃): δ 158.6, 145.1, 129.5, 119.9, 113.3, 112.8, 81.9 (d, J=169 Hz), 67 (d, J=21 Hz), 46.3.

Part C—Preparation of 3-(2-Fluoroethoxy)benzyl bis(tert-butoxycarbonyl)guanidine

A 15 mL round bottom flask was flame dried and charged with the product of Part B (0.1 g, 0.59 mmol) and this was dissolved in MeCN (3.5 mL). N,N-bis(tert-butoxycarbonyl)-1H-pyrazole-1-carboxamidine (0.183 g, 0.591 mmol) was added, the solution was stirred for 90 min, and concentrated in vacuo to a oil. This crude oil was purified by silica gel flash chromatography using dichloromethane as eluant to give 199 mg (92%) of the product as a oil. ¹H NMR (300 MHz, CDCl₃): δ 11.5 (br t, 1H), 8.4 (br t, 1H), 7.24 (d, 2H, J=9 Hz), 6.88 (d, 2H, J=9 Hz), 4.73 (t of d, 2H, J=6, 48 Hz), 4.54 (d, 2H, J=6 Hz), 4.2 (t of d, 2H, J=3, 27 Hz), 1.5 (s, 9H), 1.46 (s, 9H). ¹³C NMR (75 MHz, CDCl₃): δ 163.6, 157.9, 155.9, 153.1, 130, 129.2, 114.9, 83.1, 81.1 (d, J=169 Hz), 79.3, 67.1 (d, J=20 Hz), 44.4, 28.3, 28.

Part D—Preparation of 3-(2-Fluoroethoxy)benzylguanidinium Trifluoroacetate

The product of Part C (95 mg, 0.231 mmol) was charged to a flame dried 15 mL flask and dissolved in dioxane (0.5 mL). A solution of 4M HCl in dioxane (2.5 mL) was added followed by concentrated hydrochloric acid (0.5 mL). The reaction mixture was stirred for 16 h, and concentrated in vacuo to obtain a oil. This oil was purified by preparative HPLC (Phenomenex Luna C18(2) column 10μ, 21.2×250 mm; gradient: 0% B for 5 min then 0-30% B over 20 min at 20 mL/min; Mobile phase A=0.1% TFA in water and B=0.1% TFA in 90% water) to obtain 34 mg (52%) of the title compound. ¹H NMR (600 MHz, CDCl₃+3 drops DMSO-d₆): δ 8.0 (t, 1H, J=6 Hz), 7.1 (t, 1H, 0.1=7.8 Hz), 6.85 (m, 2H), 6.76 (1H, d of d, 0.1=8.4, 1.8 Hz), 4.67 (t of d, 2H, J=4.2, 47.4 Hz), 4.31 (d, 2H, J=6 Hz), 4.16 (t of d, 2H, J=4.2, 28.8 Hz). HRMS: Calc'd for C₁₀H₁₄FN₃O (M+H): 212.1193; Found: 212.1191.

Example 10 Synthesis of 3-Chloro-4-(2-fluoroethoxy)phenethylguanidinium Trifluoroacetate

Part A—Preparation of 3-Chloro-4-hydroxyphenethylammonium Trifluoroacetate

To a 25 mL round bottom flask was added 3-chloro-4-methoxy phenethylamine hydrochloride and this was dissolved in hydrobromic acid (6.8 mL). The solution was heated to 110° C. for 5 h after which it was concentrated and dissolved in water (5 mL). The aqueous solution was purified by preparative HPLC (Phenomenex Luna C18(2) column 10μ, 21.2×250 mm; gradient: 0% B for 10 min then 0-30% B over 30 min at 20 mL/min; Mobile phase A=0.1% TFA in water and B=0.1% TFA in 90% water) to obtain 289 mg (51%) of the title compound. ¹H NMR (600 MHz, DMSO-d₆): δ 10.1 (s, 1H), 7.8 (br, 3H), 7.23 (s, 1H), 7.01 (1H, d, J=8.4 Hz), 6.92 (d, 1H, J=8.4 Hz).

Part B—Preparation of N-(tert-Butoxycarbonyl)-3-chloro-4-hydroxyphenethylamine

To a flame dried 15 mL round bottom flask was added the product of Part A (97 mg, 0.34 mmol), followed by a mixture of dimethylformamide and dichloromethane (4 mL; 1:1) to dissolve it. Diisopropylethylamine (87.9 mg, 0.118 mL, 0.68 mmol) and di-tert-butyl dicarbonate (89 mg, 0.408 mmol) were then added successively and the mixture was stirred for 30 min. The reaction mixture was concentrated in vacuo and the crude oil subjected to silica gel flash chromatography in dichloromethane to give 72 mg (78%) of the product. ¹H NMR (600 MHz, DMSO-d₆): δ 9.85 (s, 1H), 7.12 (s, 1H), 6.93 (d, 1H, J=8.4 Hz), 6.86 (m, 1H), 6.79 (br t, 1H), 3.075 (q, 2H, J=6.6 Hz), 2.57 (t, 2H, J=7.2 Hz), 1.35 (s, 9H).

Part C—Preparation of 3-Chloro-4-(2-fluoroethoxy)phenethylammonium Trifluoroacetate

Powdered sodium hydroxide (14.2 mg, 0.356 mmol) was placed in a 15 mL round bottom flask. The product of Part B (69 mg, 0.254 mmol) was added followed by dimethylsulfoxide (2.5 mL). The resulting mixture was stirred for 5 min after which 1-p-tosyloxy-2-fluoroethane (prepared according to literature reference: J. Med. Chem. 1980, 23, 985-990) was added, and the flask immersed in a preheated oil bath at 75° C. The reaction was stirred for 60 min after which it was cooled to room temperature and diluted with dichloromethane (10 mL). The organic layer washed with water (5×6 mL) and brine, dried over magnesium sulfate, and concentrated in vacuo to give 120 mg of an oil. This oil was added a solution of trifluoroacetic acid in dichloromethane (3.0 mL, 1:1) and the resulting solution was stirred for 60 min at ambient temperature. The reaction mixture was concentrated in vacuo and subjected to preparative HPLC (Phenomenex Luna C18(2) column 10μ, 21.2×250 mm; gradient: 10-40% B over 20 min at 20 mL/min; Mobile phase A=0.1% TFA in water and B=0.1% TFA in 90% water) to obtain 52 mg (62% for two steps) of the title compound. ¹H NMR (600 MHz, DMSO-d₆): δ 7.8 (br, 2H), 7.36 (d, 1H, J=1.8 Hz), 7.19 (d of d, 1H, J=2.4, 8.4 Hz), 7.13 (d, 1H, J=8.4 Hz), 4.75 (t of d, 2H, J=4.2, 41.4 Hz), 4.32 (t of d, 2H, J=3.6, 32 Hz), 3.0 (br t, 2H), 2.8 (t, 2H, J=7.8 Hz). ¹³C NMR (150 MHz, DMSO-d₆): δ 152.3, 130.9, 130.1, 128.5, 121.4, 114.2, 81.9 (d, J=166 Hz), 68.2 (d, J=18.9 Hz). HRMS: Calc'd for C₁₀H₁₃FClNO (M+H): 218.0742; Found: 218.0743.

Part D—Preparation of 3-Chloro-4-(2-fluoroethoxy)phenethylguanidinium Trifluoroacetate

To a flame dried 5 mL flask was added product of Part C (47 mg, 0.142 mmol). To this was added MeCN (1.4 mL) and diisopropylethylamine (37 mg, 50 μL, 0.248 mmol), followed by N,N-bis(tert-butoxycarbonyl)-1H-pyrazole-1-carboxamidine (44 mg, 0.142 mmol). The solution was stirred for 90 min after which it was concentrated in vacuo to an oil. This oil was passed through a plug of silica gel and eluted with hexanes/DCM (1:1 to 1:2). The eluant was concentrated to obtain 64 mg (98%) of an oil. This oil was redissolved in trifluoroacetic acid (1 mL) and heated to 55° C. for 5 min after which it was concentrated and purified by preparative HPLC (Phenomenex Luna C18(2) column 10μ, 21.2×250 mm; gradient: 10-40% B over 20 min at 20 mL/min; Mobile phase A=0.1% TFA in water and B=0.1% TFA in 90% water) to obtain 37 mg (54% for last step) of the title compound. ¹H NMR (600 MHz, DMSO-d₆): δ 7.56 (br t, 1H), 7.38 (d, 1H, J=2.4 Hz), 7.185 (d of d, 1H, J=2.4, 8.4 Hz), 7.15 (d, 1H, J=8.4 Hz), 4.75 (t of d, 2H, J=4.2, 48 Hz), 4.3 (t of d, 2H, J=3.6, 30 Hz), 3.6 (br, 2H), 3.33 (AB q, 2H, J=6.6 Hz), 2.72 (t, 2H, J=7.8 Hz). ¹³C NMR (150 MHz, DMSO-d₆): δ 156.6, 152.1, 132., 130.2, 128.5, 121.2, 117.9, 114, 81.9 (d, J=165.9 Hz), 68.21 (d, J=18.75 Hz), 41.8, 33.1. HRMS: Calc'd for C₁₁H₁₅ClFN₃O (M+H): 260.0960; Found: 260.0962.

Example 11 Synthesis of 1-(4-Fluoro-3-hydroxyphenyl)-1-hydroxy-N-methylpropan-2-aminium Trifluoroacetate

Part A—Preparation of 1-(4-Fluoro-3-methoxyphenyl)-2-nitropropan-1-ol

To a flame dried 100 mL round bottom flask was added 3-methoxy-4-fluorobenzaldehyde (367 mg, 2.38 mmol) and this was dissolved in methanol (23 mL). The reaction solution was cooled to 0° C. and nitroethane (357 mg, 4.76 mmol) was added to it followed by 5M NaOH (0.476 mL, 2.38 mmol). The solution was stirred for 80 min at 0° C. after which acetic acid (2% solution, 32 mL) was added and stirred for an additional 30 min. The reaction mixture was concentrated and water (10 mL) was added. The solution was extracted with dichloromethane (4×20 mL). The combined organic layers were washed with brine, dried over magnesium sulfate, and concentration to give afford an oil which was purified by silica gel flash chromatography using dichloromethane as eluant. Product (391 mg, 72%) product was obtained as a colorless oil in a 1.88:1 ratio (A:B) of diastereorners. Pair A: ¹H NMR (600 MHz, CDCl₃): δ 7.07 (m, 1H), 7.0 (m, 1H), 6.8 (m, 1H), 5.34 (t, 1H, J=3 Hz), 4.65 (d of q, 1H, J=3.6, 6.6 Hz), 3.9 (s, 3H), 2.697 (d, 1H, J=3.6 Hz), 1.5 (d, 3H, J=6.6 Hz). ¹³C NMR (75 MHz, CDCl₃): δ 153.3, 150.1, 147.44 (d, J=10.8 Hz), 134.1, 117.7 (d, J=7 Hz), 115.7 (d, J=18.6 Hz), 110.6, 86.8, 72.8, 55.8, 11.7. Pair B: ¹H NMR (600 MHz, CDCl₃): δ 7.07 (m, 1H), 7.0 (m, 1H), 6.8 (m, 1H), 4.9 (d of d, 1H, J=3.6, 9 Hz), 4.72 (m, 1H), 3.9 (s, 3H), 2.57 (d, 1H, J=4.2 Hz), 1.33 (d, 3H, J=5.4 Hz). ¹³C NMR (75 MHz, CDCl₃): δ 153.8, 150.5, 147.76 (d, J=10.8 Hz), 134.1, 119 (d, J=7 Hz), 115.8 (d, J=18.6 Hz), 111, 87.7, 75.3, 55.8, 15.9. HRMS: Calc'd for C₁₀H₁₂FNO₄ (M+Na): 252.0642; Found: 252.0643.

Part B—Preparation of 1-(4-Fluoro-3-methoxyphenyl)-2-aminopropan-1-ol

The product of Part A (301 mg, 1.31 mmol) was dissolved in a mixture of tetrahydrofuran and methanol (13 mL, 1:1) in a 50 mL flame dried round bottom flask. To this solution was added Pd—C(10 wt %, 69.7 mg, 0.065 mmol) followed by ammonium formate (413 mg, 6.55 mmol). The reaction solution was stirred at ambient temperature for 20 h after which an additional 413 mg ammonium formate and 70 mg Pd—C catalyst were added. The reaction mixture was stirred an additional 3 h after which it was filtered through a pad of Celite® and the filtrate concentrated in vacuo to obtain an oil. This oil was subjected to silica gel flash chromatography (DCM/MeOH/aqueous ammonia 8.9:1:0.1) to obtain 115 mg (44%) of the product as an oil in a 2:1 (A:B) mixture of diastereomers. Pair A: ¹H NMR (600 MHz, DMSO-d₆): δ 7.0 (m, 2H), 6.84 (m, 1H), 4.1 (d, 1H, J=6.6 Hz), 3.82 (s, 3H), 2.79 (dddd, 1H, J=6.6 Hz), 0.79 (d, 3H, J=6.6 Hz). ¹³C NMR (150 MHz, CDCl₃): δ 151.2, 149.6, 146.4, 140.7, 118.65, 114.75, 112, 77.8, 55.8, 52.6, 19.3. Pair B: ¹H NMR (600 MHz, DMSO-d₆): δ 7.0 (m, 2H), 6.84 (m, 1H), 4.28 (d, 1H, J=6.6 Hz), 3.82 (s, 3H), 2.87 (dddd, 1H, J=6.6 Hz), 0.85 (d, 3H, J=6.6 Hz). ¹³C NMR (150 MHz, CDCl₃): δ 151.2, 149.6, 146.4, 140.3, 118.65, 114.75, 112, 77.0, 55.8, 52.1, 18.1. HRMS: Calc'd for C₁₀H₁₄FNO₂ (M+H): 200.1081; Found: 200.1078.

Part C—Preparation of 1-(4-Fluoro-3-methoxyphenyl)-2-(methylamino)propan-1-ol

The product of Part B (101 mg, 0.507 mmol) was dissolved in ethyl formate (10 mL) in a flame dried 50 mL round bottom flask fitted with a reflux condenser. The solution was heated at 60° C. for 16 h, concentrated in vacuo, and the crude oil obtained was purified by silica gel flash chromatography (dichloromethane/methanol/ammonia 8.9:1:0.1) to yield 101 mg of the intermediate aldehyde. This aldehyde (50 mg, 0.22 mmol) was dissolved in tetrahydrofuran (5.0 mL) and added drop-wise to a solution of lithium aluminum hydride in tetrahydrofuran (1.27 mL of a 1.0M solution) at 0° C. The reaction was stirred at 0° C. for 30 min after which the bath was removed and the solution stirred at ambient temperature for 30 min and at reflux for 30 min. The reaction was then quenched by adding 59 μL water, 59 μL 15% NaOH and finally 0.2 mL water. The suspension was stirred for 20 min, filtered, and concentrated to an oil. This oil was subjected to purification using silica gel flash chromatography (dichloromethane/methanol/ammonia 8.9:1:0.1) to yield 38 mg (81%) of product as a 2.5:1 (A:B) mixture of diastereomers. Pair A: ¹H NMR (300 MHz, DMSO-d₆): δ 7.11 (m, 2H), 6.85 (m, 1H), 4.21 (d, 1H, J=9 Hz), 3.83 (s, 3H), 2.57 (m, 1H), 2.29 (s, 3H), 0.71 (d, 3H, J=6 Hz). ¹³C NMR (75 MHz, DMSO-d₆): δ 152.1, 148.8, 146.47, 140.37 (d, J=3 Hz), 119.17 (d, J=6.75 Hz), 114.87, 112.2, 75.6, 60.5, 55.8, 33.3, 15.1. Pair B: ¹H NMR (300 MHz, DMSO-d₆): δ 7.11 (m, 2H), 6.85 (m, 1H), 4.57 (d, 1H, J=6 Hz), 3.83 (s, 3H), 2.62 (m, 1H), 2.29 (s, 3H), 0.79 (d, 3H, J=6 Hz). ¹³C NMR (75 MHz, DMSO-d₆): δ 151.7, 148.5, 146.47, 140.6 (d, J=3 Hz), 118.29 (d, J=6.75 Hz), 114.87, 111.68, 72.7, 60.0, 55.8, 33.3, 13.95. HRMS: Calc'd for C₁₁H₁₆FNO₂ (M+H): 214.1237; Found: 214.1239.

Part D—Preparation of 1-(4-Fluoro-3-hydroxyphenyl)-1-hydroxy-N-methylpropan-2-aminium Trifluoroacetate

To a flame dried 15 mL round bottom flask was added the product of Part C (30 mg, 0.141 mmol) and this was dissolved in dichloromethane (2.0 mL). The contents were cooled to −78° C. and a solution of boron tribromide (0.353 mL, 1.0M in DCM) was added drop-wise. The reaction mixture was stirred for 5 h after which it poured into a beaker containing cold water (2 mL) and stirred for another 1 hr. This mixture was then poured into a separatory funnel and the layers separated. The organic layer was washed with saturated sodium bicarbonate and extracted with 2M NaOH (3×5 mL). The combined NaOH solution was then acidified to pH 3 using 5N HCl and extracted with dichloromethane (3×10 mL). The aqueous layer was lyophilized to obtain a solid which was triturated with a MeCN/water mixture (10 mL, 1:1). This mixture was subjected to preparative HPLC ((Phenomenex Luna C18(2) column 10μ, 21.2×250 mm; gradient: 10% B for 10 min the 10-30% B over 20 min at 20 mL/min; Mobile phase A=0.1% TFA in water and B=0.1% TFA in 90% water) to obtain 20 mg (45%) of the title compound as a 2:1 (A:B) mixture of diastereomers. Pair A: ¹H NMR (600 MHz, DMSO-d₆): δ 9.99 (s, 1H), 8.52 (br, 1H), 7.13 (m, 1H), 6.9 (m, 1H), 6.77 (m, 1H), 6.3 (d, 1H, J=3.6 Hz), 4.4 (d, 1H, J=6 Hz), 3.3 (br, 1H), 2.5 (s, 3H), 0.95 (d, 3H, J=6.6 Hz). ¹³C NMR (150 MHz, DMSO-d₆): δ 149.9, 144.75 (d, J=12.3 Hz), 137.5, 117.8, 116.2, 115.5, 72.6, 58, 48, 29, 11.9. Pair B: ¹H NMR (600 MHz, DMSO-d₆): δ 9.90 (s, 1H), 8.38 (br, 1H), 7.13 (m, 1H), 6.9 (m, 1H), 6.77 (m, 1H), 6.1 (d, 1H, J=3.6 Hz), 4.9 (br t, 1H), 3.21 (br t, 1H), 2.59 (s, 3H), 0.91 (d, 3H, J=6.6 Hz). ¹³C NMR (150 MHz, DMSO-d₆): δ 149.3, 144.5 (d, J=12.3 Hz), 137.3, 116.4, 116.2, 115.5, 69, 58, 48, 30.4, 9.1. HRMS: Calc'd for C₁₀H₁₄FNO₂ (M+H): 200.1081; Found: 200.1081.

Example 12 Norepinephrine Transporter Binding Assay

Inhibitors to be tested were dissolved in incubation buffer (50 mM Tris-HCl, 10% sucrose, pH 7.4) at appropriate dilutions. The inhibitor solutions were added to the wells of a microtiter plate (40 μL/well) in triplicate. Each well of test agent (and appropriate control wells) was treated with a mixture of MDCK cell membrane preparation (22.4 μg of membrane) expressing human norepinephrine transporter (Bmax=3.7 pmol norepinephrine transporter/mg protein), and [³H]desipramine (2 nM, 64.8 Ci/mmol) in a total volume of 0.2 mL. The resulting mixtures were incubated for 2 h on ice. A 96 well GF/C filter plate was presoaked with coating buffer (0.5% polyvinylpyrrolidine and 0.1% Tween 20) for 2 h at room temperature. The presoaked filter plate was washed with incubation buffer (6×0.2 mL). The NET reactions were transferred to the coated filter plate and filtered. The filter plate was washed (6×0.2 mL) with ice cold wash buffer (50 mM Tris-HCl, 0.9% NaCl, pH 7.4). The plate was dried overnight, incubated briefly with 25 μL scintillant, and read on a Micro Beta plate reader.

TABLE 1 NET Affinity of Examples 1-11 Example # NET Affinity, μM 1 17.94 2 <20 3 1.45 4 7.27 5 4.10 6 102.8 7 20.71 8 5.65 9 4.36 10 1.80 11 54.85

Examples 13-15 General Procedure for [¹⁸F]Fluorination via [¹⁸F]2-Fluoroethyl Tosylate Part A—Preparation of [¹⁸F]2-Fluoroethyl Tosylate

An MP1 anion exchange cartridge containing 1,000 mCi of [¹⁸F]NaF was eluted with 0.20% aqueous K₂CO₃ (1.0 mL) into a 25 mL conical-bottomed silanized flask using an automated liquid handling system. The solution was evaporated by applying a gentle stream of heated He_((g)) and applied vacuum. The contents of the flask were reconstituted with 0.5 mL of MeCN, and the MeCN was removed by heated He_((g)) and applied vacuum to eliminate residual H₂O (azeotropic evaporation). A separate 5 mL conical-bottomed Wheaton™ vial was used to prepared a solution of 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (22.5 mg) (referred to as Kryptofix™ and henceforth abbreviated as K₂₂₂) and ethylene di-(p-toluenesulfonate) (3.0 mg) in MeCN (1.0 mL). The constituents of the vial were transferred to the 25 mL flask containing [¹⁸F]KF, and the flask was positioned inside a microwave cavity (model 520 Resonance Instruments, Skokie, Ill.) and subjected to microwave radiation for 3 min at a power setting of 100 watts. The contents of the microwave reaction vial were filtered through an anion exchange resin to remove residual fluoride ion and collected in a conical-bottomed 5 mL Wheaton™ reaction vial.

Part B—[¹⁸F]Fluorination Via [¹F]2-Fluoroethyl Tosylate

The product of Part A was transferred to a conical-bottomed 5 mL Wheaton™ reaction vial containing the product of either Example 8, Example 9 or Example 10 (4.0 mg) dissolved in anhydrous DMSO (300 μL). The contents of the vial were heated at 85° C. for 30 min and cooled to ambient temperatures. The solution was treated with TFA (1.5 mL) and stirred for 30 min at ambient temperature. The solution was transferred to a clean 25 mL pear-shaped flask and diluted with H₂O (18.5 mL). The contents of the pear shaped flask were passed through a Sep Pak™ C18 cartridge and the cartridge was rinsed with H₂O (5.0 mL). The desired product was eluted from the cartridge with MeCN (3.0 mL) into a conical-bottomed 5 mL Wheaton™ vial. The product solution was purified by HPLC using a Phenomenex LUNA C18(2) column (250×10 mm, 5 micron particle size, 100 Angstrom pore size) using a 5.0%/min gradient of 0-100% ACN containing 0.1% formic acid at a flow rate of 2.0 mL/min. The product eluted from the column in 13-14 min and was collected into a pear shaped flask. The solvent was evaporated with gentle heating under vacuum. The contents of the flask were reconstituted with 10% aqueous ethanol solution for biological experiments. The final product yield was ˜50 mCi (not decay corrected). Radiochemical purity and decay corrected radiochemical yield data is shown in Table 2. Radiosynthesis and purification time was ˜150 min.

TABLE 2 Radiochemical Yield and Purity Radiochemical Radiochemical Example # Cold Example # Yield, % Purity, % 13 8 7.4 100 14 9 10.0 100 15 10 5.0 100

Example 16-22 Synthesis of Fluorinated Piperazines General Synthesis of Fluorinated CAAP Analogs

Substituted anilines can be alkylated with bis(2-chloroethyl)amine at elevated temperatures to yield the phenyl piperazine with the desired substitution pattern on the phenyl ring. The yield for this transformation is often moderate to low (<50% yield), however various phenyl piperazines are commercially available. Introduction of the guanidine moiety was carried out via alkylation of the piperazine moiety with N,N-′bis(tert-butoxycarbonyl-1H-pyrazole) 1-carbonxamidine. Deprotection of the guanidine functionality with HCl afforded the final compounds, which did not contain a fluoroethoxy moiety. For compounds where R is defined as a fluoroethoxy moiety alkylation of the hydroxyl precursor with fluoroethyl tosylate affords the desired substitution pattern. Typically ¹⁸F compounds are made by the nucleophilic displacement of an appropriate leaving group, e.g., tosylate, mesylate, trifluoromethane sulfonate, nitro, trimethyl ammonium or a halide. Alternatively a cyclic sulfate or an epoxide may also be used as a leaving group. Typically these compounds are made from highly activated, dry K¹⁸F, that is made “hotter” by the addition of cryptands such as krytofix[2.2.2]. Purification is generally via salt removal by reverse-phase chromatography (Sep-Pak).

R, R₁ and R₂ are independently selected from the list of H, OR₃, F, Cl, Br, I, CH₂F, OCH₂CH₂F, alkyl (C₁-C₄), aryl, heteroaryl, aralkyl, alkylarl, C(═O)R₃, CO₂R₃, Im, OCH₂CH₂Im, and XIm. Im is an imaging moiety and may be selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, and ¹³¹I. R₃ may be selected from the same list as R-R₂. The alkyl, aryl or heteroaryl substituents in turn may be substituted with alkyl(C₁-C₄), Im, —(CH₂)_(n)Im, CO₂H, halogen (F, Cl, Br, I), OH, NH₂, COOH, Im, COOR, CONR₂, SR, OR or NR₂, in which R may be hydrogen alkyl, aryl or alkylaryl. Under physiological conditions, the guandine/amidine functionality of the invention may be protonated; the corresponding salts of the compounds are also included (hydrochloride, hydrobromide, sulfate, nitrate, alkyl/aryl sulfonates).

Example 16 Synthesis of 4-(4-fluorophenyl)piperazine-1-carboximidamide

To a solution of 4-(fluorophenyl)piperazine (100 mg, 0.56 mmol) and diisopropylethylamine (106 μL, 0.61 mmol) in ACN (2 mL) was added 1H-pyrazole-1-carboximidamide hydrochloride (89 mg, 0.61 mmol). The reaction stirred at room temperature overnight. A precipitate formed, which was collected via filtration and washed with ACN to obtain 4-(4-fluorophenyl)piperazine-1-carboximidamide as a white solid (119 mg, 97% yield). ¹H NMR (300 MHz, DMSO-d6): δ 7.77 (br s, 3H), 7.10-6.97 (m, 4H), 3.60 (dd, 4H, J=5.3, 4.7 Hz), 3.14 (dd, 4H, J=5.4, 4.7 Hz); ¹³C NMR (75.5 MHz, DMSO-d6): δ 157.9 (154.8), 156.3, 147.2, 118.0, 115.5 (115.2), 48.3, 44.7; ¹⁹F NMR (282.4 MHz, DMSO-d6): δ −124.70-124.78 (m, 1F); HRMS calcd for C₁₁H₁₅FN₄: 223.13535 found 223.1353.

Example 17 Synthesis of 4-(3-(fluoromethyl)phenyl)piperazine-1-carboximidamide

Synthesis of 4-(3-hydroxymethyl-phenyl)-piperazine-1-carboxylic acid tert-butyl ester

To a solution of 4-(3-formyl-phenyl)-piperazine-1-carboxylic acid tert-butyl ester (2.0 g, 5.98 mmol) in THF (14 mL) at 0° C. was added LAH (6.0 mL, 1M solution in THF). The reaction mixture stirred at 0° C. for 30 min. followed by a quench of H₂O (239 μL), 15% NaOH (aq., 239 μL), and H₂O (718 μL). After completion of the additions the mixture stirred for 20 min. and was then filtered over a pad of celite. The solvent of the filtrate was removed en vacuo to obtain 4-(3-hydroxymethyl-phenyl)-piperazine-1-carboxylic acid tert-butyl ester as a brown solid (1.47 g, 84% yield), which was taken on to the next reaction without further purification. ¹H NMR (300 MHz, DMSO-d6): δ 7.17 (t, 1H, J=8.0 Hz), 6.91 (br s, 1H), 6.82-6.76 (m, 2H), 5.06 (t, 1H, J=5.80 Hz), 4.44 (d, 2H, J=5.6 Hz), 3.45 (dd, 4H, J=5.5, 4.9 Hz), 3.08 (dd, 4H, J=5.3, 5.1 Hz), 1.42 (s, 9H).

Synthesis of tert-butyl 4-(3-fluoromethyl-phenyl)-piperazine-1-carboxylic acid tert-butyl ester

To a solution of 4-(3-hydroxymethyl-phenyl)-piperazine-1-carboxylic acid tert-butyl ester (200 mg, 0.68 mmol), triethylamine (143 μL, 1.03 mmol), and tetramethylethylenediamine (10 μL, 0.07 mmol) in toluene (2 mL) at 0° C. was added methanesulfonyl chloride (79 μL, 1.03 mmol) drop-wise. After completion of addition the reaction mixture stirred at 0° C. for 40 min. EtOAc (5 mL) was added to the reaction mixture and the organic layer was separated, washed with brine, dried over Na₂SO₄, and concentrated to obtain 4-(3-(methanesulfonyloxymethyl-phenyl)-piperazine-1-carboxylic acid tert-butyl ester as a brown oil.

In a Wheaton vial TBAF (268 mg, 1.03 mmol) was added to a solution of crude 4-(3-(methanesulfonyloxymethyl-phenyl)-piperazine-1-carboxylic acid tert-butyl ester in ACN (2.3 mL). After completion of addition the reaction mixture was heated to 130° C. for 10 min. before being quenched with water (1.0 mL). The reaction mixture was extracted with EtOAc (3×5.0 mL) and the organic layers were washed with brine, dried over Na₂SO₄, and concentrated to obtain tert-butyl 4-(3-(fluoromethyl)phenyl)piperazine-1-carboxylate along with minor impurities (201.3 mg, 100% crude yield). ¹H NMR (300 MHz, DMSO-d6): δ 7.29-7.24 (m, 1H), 6.99-6.94 (m, 2H), 6.86-6.84 (m, 1H), 5.34 (d, J=48 Hz, 2H), 3.47-3.44 (m, 4H), 3.13-3.10 (m, 4H), 1.42 (s, 9H).

Synthesis of 4-(3-(fluoromethyl)phenyl)piperazine-1-carboximidamide

Tert-butyl 4-(3-(fluoromethyl)phenyl)piperazine-1-carboxylate (201.3 mg, mmol) was dissolved in a 4.0M solution of HCl and dioxane (2 mL) and stirred at room temperature. After 45 min. the reaction mixture was concentrated and re-dissolved in ACN (2 mL). Diisopropylethylamine (22 μL, 1.51 mmol) and 1H-pyrazole-1-carboximidamide (110 mg, 0.75 mmol) were added to the stirring reaction mixture. The next day, the reaction mixture was concentrated to yield a crude oil, which was purified by HPLC using a Phenomenex Luna C-18 (2) column (10μ, 250×21.2 mm, gradient method 0-100% B over 14 min., where B=90% ACN in water using 0.1% TFA as a modifier and A=water using 0.1% TFA as a modifier) with a flow rate of 20 mL/min to isolate 4-(3-(fluoromethyl)phenyl)piperazine-1-carboximidamide as a white solid (42.7 mg, 23% isolated yield over 4 steps). ¹H NMR (300 MHz, DMSO-d6): δ 7.58 (br s, 3H), 7.28 (t, 1H, J=7.8 Hz), 7.01 (br s, 1H), 6.98 (br s, 1H), 6.87 (d, 1H, J=7.3 Hz), 5.35 (d, 2H, J=47.9 Hz), 3.58 (dd, 4H, J=5.4, 4.9 Hz), 3.26 (dd, 4H, J=5.4, 4.8 Hz); ¹³C NMR (75.5 MHz, DMSO-d6): δ 156.1, 150.3, 137.1 (136.8), 129.2, 118.8 (118.7), 115.9, 114.9 (114.8), 84.6 (83.4), 47.2, 44.7; HRMS calcd for C₁₂H₁₇FN₄: 237.15100 found 237.1514.

Example 18 Synthesis of 4-[4-(2-fluoro-ethoxy)-phenyl]-piperazine-1-carboxamidine

Synthesis of tert-butyl 4-(4-(2-fluoroethoxy)phenyl)piperazine-1-carboxylate

To a solution of 4-hydroxyphenylpiperazine (2.0 g, 11.22 mmol) in water (56 mL) was added NaOH (673 mg, 16.83 mmol) followed by di-tert-butyl dicarbonate (2.7 g, 12.34 mmol). The reaction mixture stirred at room temperature overnight. The next day, the reaction mixture was filtered to collect tert-butyl 4-(4-hydroxyphenyl)-piperazine-1-carboxylate as a tan solid (3.1 g, 99% yield), which was washed with water (50 mL) and taken on to the next step without further purification. ¹H NMR (300 MHz, DMSO-d6): δ 6.79 (AA′BB′, 2H, J_(AB)=9.1 Hz, J_(AA′)=2.4 Hz), 6.66 (AA′BB′, 2H, J_(AB)=9.1 Hz, J_(BB′)=2.4 Hz), 3.43 (dd, 4H, J=5.3, 4.9 Hz), 2.88 (dd, 4H, J=5.2, 5.1 Hz), 1.41 (s, 9H); ¹³C NMR (75.5 MHz, DMSO-d6): δ 153.8, 151.4, 144.0, 118.5, 115.4, 78.8, 50.3, 28.0.

To a solution of tert-butyl 4-(4-hydroxyphenyl)-piperazine-1-carboxylate (1.0 g, 3.59 mmol) in DMSO (12 mL) was added potassium carbonate (745 mg, 5.39 mmol), potassium iodide (18 mg, 0.11 mmol) and 1-bromo-2-fluoroethane (294 μL, 3.95 mmol). The reaction stirred at 50° C. overnight. The next day, additional amounts of potassium carbonate (745 mg, 5.39 mmol), 1-bromo-2-fluoroethane (134 μL, 1.79 mmol), and potassium iodide (18 mg, 0.11 mmol) were added. The reaction mixture continued to stir at 50° C. After 5 h the reaction mixture was cooled to room temperature, quenched with water (10 mL), and extracted with EtOAc (3×50 mL). The combined organic layers were washed with water (100 mL), brine (50 mL), dried over Na₂SO₄, and concentrated to obtain a brown solid. The crude material was purified using silica gel chromatography (1:4 hexanes: EtOAc) to obtain tert-butyl 4-(4-(2-fluoroethoxy)phenyl)piperazine-1-carboxylate as a white solid (440 mg, 38% yield). ¹H NMR (300 MHz, DMSO-d6): δ 6.92-6.84 (m, 4H), 4.78 (m, 1H), 4.62 (m, 1H), 4.20 (m, 1H), 4.10 (m, 1H), 3.45 (dd, 4H, J=5.2, 5.0 Hz), 2.96 (dd, 4H, J=5.3, 5.0 Hz), 1.42 (s, 9H); ¹⁹F NMR (282.4 MHz, DMSO-d6): δ −222.04 (m, 1F); ¹³C NMR (75.5 MHz, DMSO-d6): δ 153.8, 152.1, 145.5, 117.9, 115.1, 83.2 (81.1), 78.9, 67.4 (67.2), 49.7, 43.2, 28.0; HRMS calcd. for C₁₇H₂₅FN₂O₃: 325.19220 found 325.19230.

Synthesis of 4-[4-(2-fluoro-ethoxy)-phenyl]-piperazine-1-carboxamidine

A solution of tert-butyl 4-(4-(2-fluoroethoxy)phenyl)piperazine-1-carboxylate (440 mg, 1.36 mmol) in 4.0M HCl in Dioxane (7 mL) stirred for 30 min. at room temperature. A precipitate formed, which was collected via filtration and washed with Dioxane to obtain the desired product as a white powder. The crude material was purified on the Prep HPLC using a 0-100% B over 14 min. method (% B=0.1% TFA in 90% ACN). The pure fractions were collected and lyophilized overnight to afford 1-(4-(2-fluoroethyl)phenyl)-piperazine as a white cake TFA salt (362 mg, 79% yield). ¹H NMR (300 MHz, DMSO-d6): δ 9.00 (br s, 1H), 6.97-6.87 (m, 4H), 4.78 (m, 1H), 4.62 (m, 1H), 4.21 (m, 1H), 4.11 (m, 1H); 3.22 (s, 8H) ¹⁹F NMR (282.4 MHz, DMSO-d6): δ −222.07 (m, 1F); ¹³C NMR (75.5 MHz, DMSO-d6): 152.5, 144.5, 118.0, 115.2, 83.3 (81.1), 67.4 (67.2), 46.7, 42.8; HRMS calcd. for C₁₂H₁₇FN₂O: 225.13977 found: 225.13961.

To a solution of 1-(4-(2-fluoroethoxy)phenyl)piperazine (50 mg, 0.15 mmol) and diisopropylethylamine (59 μL, 0.34 mmol) in ACN (1 mL) was added 1H-pyrazole-1-carboximidamide (25 mg, 0.17 mmol). The reaction stirred at room temperature for 1 h, monitored by LC-MS. The precipitate was then filtered and washed with ACN to obtain the desired product as a white solid (33.8 mg, 58% yield). ¹H NMR (300 MHz, DMSO-d6): δ 7.55 (br s, 3H), 6.95-6.86 (m, 4H), 4.78 (m, 1H), 4.62 (m, 1H), 4.21 (m, 1H), 4.11 (m, 1H), 3.57 (dd, 4H, J=5.2, 4.9 Hz), 3.09 (dd, 4H, J=5.1, 5.0 Hz); ¹⁹F NMR (DMSO-d6): δ −222.037 (m, 1F); ¹³C NMR (75.5 MHz, DMSO-d6): δ 156.0, 152.2, 144.9, 119.2, 115.1, 82.2 (81.1), 67.4 (67.2), 48.9, 44.9; HRMS calcd. for C₁₂H₁₇FN₂O: 267.16157 found 267.16146.

Example 19 Synthesis of 4-(3-chloro-4-(2-fluoroethoxy)phenyl)piperazine-1-carboximidamide

Synthesis of 4-(3-chloro-4-(2-fluoroethoxy)phenyl)piperazine-1-carboximidamide

To a solution of 4-amino-2-chlorophenol (1.0 g, 6.97 mmol) in n-butanol (2 mL) was added bis(2-chloroethyl)amine hydrochloride (1.2 g, 6.97 mmol). After completion of addition the reaction mixture was heated at reflux for 60 h. Solid Na₂CO₃ (740 mg, 6.97 mmol) was added to the hot reaction mixture in one portion and the reaction mixture continued stirring at reflux. After 7 h the reaction mixture was cooled to RT and 2-chloro-4-(piperazin-1-yl)phenol was collected via filtration. The purple solid was washed with heptanes before proceeding to the next step without further purification (554 mg, 37% yield). ¹H NMR (300 MHz, DMSO-d6): δ 6.95 (dd, 1H, J=2.8, 1.9 Hz), 6.91 (s, 1H), 6.81 (m, 1H), 3.21 (m, 4H), 3.16 (m, 4H).

Synthesis of tert-butyl (4-(3-chloro-4-hydroxyphenyl)piperazin-1-yl)methanediylidenedicarbamate

To a solution of 2-chloro-4-(piperazin-1-yl)phenol (200 mg, 0.94 mmol) and diisopropylethylamine (180 μL, 1.03 mmol) in DMF (3 mL) was added tert-butyl (1H-pyrazol-1-yl)methanediylidenedicarbamate (321 mg, 1.03 mmol). After stirring at room temperature for 1.5 h the reaction mixture was diluted with water (10 mL) and extracted with EtOAc (3×20 mL). The organic layers were separated and washed with brine, dried over Na₂SO₄, and concentrated to yield a crude oil. Purification of the crude material using silica gel chromatography (gradient of 20 to 100% EtOAc in hexanes) afforded tert-butyl (4-(3-chloro-4-hydroxyphenyl)piperazin-1-yl)methanediylidenedicarbamate as an oil, which crystallized upon standing (186 mg, 43% yield). ¹H NMR (300 MHz, DMSO-d6): δ 9.61 (s, 1H), 9.48 (s, 1H), 6.91 (d, 1H, J=2.8 Hz), 6.86 (m, 1H), 6.79 (dd, 1H, J=8.9, 2.8 Hz), 3.50 (dd, 4H, J=5.2, 4.3 Hz), 2.99 (dd, 4H, J=5.0, 4.8 Hz), 1.42 (s, 9H), 1.37 (s, 9H); ¹³C NMR (75.5 MHz, DMSO-d6): δ 159.7, 151.2, 150.8, 146.6, 144.5, 119.8, 117.9, 116.9, 116.7, 80.1, 77.1, 49.2, 45.3, 27.9 (2C); HRMS calcd. for C₂₁H₃₁ClN₄O₅: 455.20557 found 455.20573.

Synthesis of tert-butyl (4-(3-chloro-4-(2-fluoroethoxy)phenyl)piperazin-1-yl)methanediylidenedicarbamate

To a solution of Tert-butyl (4-(3-chloro-4-hydroxyphenyl)piperazin-1-yl)methanediylidenedicarbamate (182 mg, 0.40 mmol) in DMSO (4 mL) was added potassium carbonate (83 mg, 0.60 mmol), potassium iodide (3 mg, 0.02 mmol), and 1-bromo-2-fluoroethane (33 μL, 0.44 mmol). After completion of the additions the reaction mixture stirred at 50° C. After 4.5 h the reaction mixture was cooled to room temperature and quenched with water (10 mL). The aqueous layer was extracted with EtOAc (4×20 mL) and all combined organic layers were washed with water (50 mL), brine (50 mL), dried over Na₂SO₄, and concentrated to yield a crude oil.

Purification of the crude material via HPLC using a Phenomenex Luna C-18 (2) column (10μ, 250×21.2 mm, gradient method 40-80% B over 20 min., where B=90% ACN in water using 0.1% formic acid as a modifier and A=water using 0.1% formic acid as a modifier) with a flow rate of 20 mL/min to obtain tert-butyl (4-(3-chloro-4-(2-fluoroethoxy)phenyl)piperazin-1-yl)methanediylidenedicarbamate as a white solid (28.8 mg, 12% yield based on recovered starting material). ¹H NMR (300 MHz, DMSO-d6): δ 9.62 (s, 1H), 7.06 (d, 1H, J=9.1 Hz), 7.04 (d, 1H, J=2.9 Hz), 6.89 (dd, 1H, J=9.0, 2.9 Hz), 4.75 (m, 1H), 4.67 (m, 1H), 4.25 (m, 1H), 4.20 (m, 1H), 3.51 (dd, 4H, J=6.1, 4.1 Hz), 3.08 (dd, 4H, J=5.1, 4.8 Hz), 1.42 (s, 9H), 1.37 (s, 9H); ¹⁹F NMR (282.4 MHz, DMSO-d6): δ −222.03 (m, 1F); ¹³C NMR (75.5 MHz, DMSO-d6): δ 159.7, 151.2, 150.7, 147.1, 145.9, 122.3, 117.9, 115.7, 115.6, 82.1 (81.6), 80.1, 77.1, 68.8 (68.7), 48.6, 45.1, 27.9 (2C) Minor rotomeric population is also visible; HRMS calcd. for C₂₃H₃₄ClFN₄O₅: 501.22745 found 501.2272.

Synthesis of 4-(3-chloro-4-(2-fluoroethoxy)phenyl)piperazine-1-carboximidamide

Tert-butyl (4-(3-chloro-4-(2-fluoroethoxy)phenyl)piperazin-1-yl)methanediylidenedicarbamate (26 mg, 0.05 mmol) was dissolved in a 4.0M solution of HCl in dioxane (0.5 mL) and stirred at room temperature overnight. The next day the reaction mixture was concentrated to yield a crude oil. Purification of the crude material via HPLC using a Phenomenex Luna C-18 (2) column (10μ, 250×21.2 mm, gradient method 0-100% B over 14 min., where B=90% ACN in water using 0.1% TFA as a modifier and A=water using 0.1% TFA as a modifier) with a flow rate of 20 mL/min afforded 4-(3-chloro-4-(2-fluoroethoxy)phenyl)piperazine-1-carboximidamide as a white solid (22 mg). ¹H NMR (DMSO-d6): δ 7.53 (br s, 3H), 7.09 (d, 1H, J=2.8 Hz), 7.07 (d, 1H, J=8.1 Hz), 6.93 (dd, 1H, J=9.1, 2.9 Hz), 4.80 (m, 1H), 4.64 (m, 1H), 4.28 (m, 1H), 4.18 (m, 1H), 3.55 (dd, 4H, J=5.1, 4.9 Hz), 3.14 (dd, 4H, J=5.6, 4.4 Hz); ¹⁹F NMR (282.4 MHz, DMSO-d6): δ −222.03 (m, 1F); ¹³C NMR (75.5 MHz, DMSO-d6): δ 155.9, 147.2, 145.5, 122.3, 117.9, 115.8, 115.5, 82.7 (81.6), 68.8 (68.7), 48.1, 44.7; HRMS calcd. for C₁₃H₁₈ClFN₄O: 301.12259 found 301.1225.

Example 20 Synthesis of 4-(3-Bromo-4-(2-fluoroethoxy)phenyl)piperazine-1-carboximidamide

Synthesis of tert-butyl (4-(3-bromo-4-hydroxyphenyl)piperazin-1-yl)methanediylidenedicarbamate

To a solution of the 4-amino-2-bromophenol (1.0 g, 5.32 mmol) in n-butanol (5 mL) was added bis(2-chloroethyl)amine hydrochloride (949 mg, 5.32 mmol). After completion of addition, the reaction mixture was heated at reflux for 60 h. Solid Na₂CO₃ (564 mg, 5.32 mmol) was added to the hot reaction mixture in one portion and the reaction mixture continued stirring at reflux. After 7 h the reaction mixture was cooled to RT and 2-bromo-4-(piperazin-1-yl)phenol was collected via filtration. The purple solid was washed with heptanes before proceeding to the next step without further purification.

To a solution of 2-bromo-4-(piperazin-1-yl)phenol (500 mg, 1.95 mmol) and diisopropylethylamine (373 μL, 2.14 mmol) in DMF (6 mL) was added the tert-butyl (1H-pyrazol-1-yl)methanediylidenedicarbamate (664 mg, 2.14 mmol). After stirring at room temperature for 45 min. the reaction mixture was diluted with water (20 mL) and extracted with EtOAc (3×50 mL). The organic layers were separated and washed with brine, dried over Na₂SO₄, and concentrated to yield a crude oil. Purification of the crude material using silica gel chromatography (gradient of 0% to 100% EtOAc in hexanes) afforded tert-butyl (4-(3-bromo-4-hydroxyphenyl)piperazin-1-yl)methanediylidenedicarbamate was obtained as a white foam (171 mg, 40% yield). ¹H NMR (300 MHz, DMSO-d6): δ 9.64, (br s, 1H), 9.60 (s, 1H), 7.05 (br s, 1H), 6.84 (br s, 2H), 3.49 (dd, 4H, J=5.0, 4.4 Hz), 2.99 (dd, 4H, J=4.5, 4.3 Hz), 1.44-1.37 (m, 18H); ¹³C (75.5 MHz, DMSO-d6): δ 159.5, 151.2, 150.8, 147.7, 144.7, 120.8, 117.5, 116.6, 109.5, 80.1, 77.1, 49.3, 45.3, 27.9 (2C); Minor rotomeric population is also visible; HRMS calcd for C₂₁H₃₁BrN₄O₅: 499.15506 found 499.15446.

Synthesis of tert-butyl (4-(3-bromo-4-(2-fluoroethoxy)phenyl)piperazin-1-yl)methanediylidenedicarbamate

To a solution of tert-butyl (4-(3-bromo-4-hydroxyphenyl)piperazin-1-yl)methanediylidenedicarbamate (110 mg, 0.22 mmol) in DMSO (2.2 mL) was added potassium carbonate (46 mg, 0.33 mmol), potassium iodide (2 mg, 0.01 mmol), and 1-bromo-2-fluoroethane (18 μL, 0.24 mmol). After completion of the additions the reaction mixture stirred at 50° C. After 6 h the reaction mixture was cooled to room temperature and quenched with water (5 mL). The aqueous layer was extracted with EtOAc (4×20 mL) and all combined organic layers were washed with water (50 mL), brine (50 mL), dried over Na₂SO₄, and concentrated to yield a crude oil.

Purification of the crude material via HPLC using a Phenomenex Luna C-18 (2) column (10μ, 250×21.2 mm, gradient method 40-80% B over 20 min., where B=90% ACN in water using 0.1% formic acid as a modifier and A=water using 0.1% formic acid as a modifier) with a flow rate of 20 mL/min afforded tert-butyl (4-(3-bromo-4-(2-fluoroethoxy)phenyl)piperazin-1-yl)methanediylidenedicarbamate as a white solid (19 mg, 15% yield). ¹H NMR (300 MHz, DMSO-d6): δ 9.56 (s, 1H), 7.05 (d, 1H, J=2.5 Hz), 6.91-6.82 (m, 2H), 4.83 (m, 1H), 4.67 (m, 1H), 4.26 (m, 1H), 4.17 (m, 1H), 3.79 (dd, 4H, J=4.7, 4.6 Hz), 3.08 (dd, 4H, J=4.5, 4.6 Hz), 1.49 (s, 18H); ¹⁹F NMR (282.4 MHz, DMSO-d6): δ −222.03 (m, 1F); ¹³C NMR (150 MHz, CDCl₃): δ 152.6, 150.9, 150.2, 145.6, 122.9, 117.6, 115.8, 113.8, 85.0, 82.5 (81.3), 69.6 (69.4), 50.3, 49.3, 27.8; HRMS calcd for C₂₃H₃₄BrFN₄O₅: 501.22745 found 501.2272.

Synthesis of 4-(3-bromo-4-(2-fluoroethoxy)phenyl)piperazine-1-carboximidamide

Tert-butyl (4-(3-bromo-4-(2-fluoroethoxy)phenyl)piperazin-1-yl)methanediylidenedicarbamate (26 mg, 0.044 mmol) was dissolved in a 4.0M solution of HCl in dioxane (0.6 mL) and stirred at room temperature overnight. The next day the reaction mixture was concentrated and purified via HPLC using a Phenomenex Luna C-18 (2) column (10μ, 250×21.2 mm, gradient method 40-80% B over 20 min., where B=90% ACN in water using 0.1% formic acid as a modifier and A=water using 0.1% formic acid as a modifier) with a flow rate of 20 mL/min afforded 4-(3-bromo-4-(2-fluoroethoxy)phenyl)piperazine-1-carboximidamide as a white solid (7.4 mg, 44% yield). ¹H NMR (300 MHz, DMSO-d6): δ 8.45 (br s, 3H), 7.22 (d, 1H, J=2.8 Hz), 7.00 (m, 2H), 4.80 (m, 1H), 4.64 (m, 1H), 4.28 (m, 1H), 4.18 (m, 1H), 3.52 (dd, 4H, J=5.4, 4.6 Hz), 3.12 (dd, 4H, J=5.3, 4.9 Hz); ¹⁹F NMR (282.4 MHz, DMSO-d6): δ −222.03 (m, 1F); ¹³C NMR (75.5 MHz, DMSO-d6): δ 156.7, 148.2, 145.9, 120.8, 116.5, 115.2, 111.9, 82.7 (81.6), 68.9 (68.8), 48.3, 44.4; HRMS calcd for C₁₃H₁₈BrFN₄O: 301.12259 found 301.1225.

Example 21 Synthesis of 4-(4-((2-fluoroethoxy)methyl)phenyl)piperazine-1-carboximidamide

Synthesis of tert-butyl 4-(4-(hydroxymethyl)phenyl)piperazine-1-carboxylate

To a cooled (0° C.) solution of tert-butyl 4-(4-formylphenyl)piperazine-1-carboxylate (1.0 g, 3.44 mmol) in ether (17 mL) and THF (3 mL) was added solid lithium borohydride (38 mg, 1.72 mmol) in one portion. The reaction mixture stirred for 1 h at 0° C. before being quenched with 1N HCl to reach pH=7. The resulting organic layer was filtered through a pad of celite and concentrated to obtain tert-butyl 4-(4-(hydroxymethyl)phenyl)piperazine-1-carboxylate as an orange solid (1 g) ¹H NMR (300 MHz, CDCl₃): δ 7.30 (d, 2H, J=8.6 Hz), 6.93 (d, 2H, J=8.6 Hz), 4.61 (d, 2H, J=5.0 Hz), 3.59 (dd, 4H, J=5.3, 5.1 Hz), 3.14 (dd, 4H, J=5.2, 5.0 Hz), 1.49 (m, 9H); ¹³C NMR (150 MHz, CDCl₃): δ 154.94, 151.11, 132.92, 128.59, 116.84, 80.14, 65.24, 49.66, 43.48, 28.64; Minor rotomeric populations are also visible; HRMS calcd for C₁₆H₂₄N₂O₃: 293.185969 found 293.18590.

Synthesis of tert-butyl 4-(4-((2-fluoroethoxy)methyl)phenyl)piperazine-1carboxylate

To a solution of tert-butyl 4-(4-(hydroxymethyl)phenyl)piperazine-1-carboxylate (100 mg, 0.34 mmol) in THF (1 mL) was added triphenylphosphine (135 mg, 0.51 mmol), 2-fluoroethanol (24 μL, 0.41 mmol) and diisopropylazodicarboxylate (99 μL, 0.51 mmol). The reaction mixture stirred at room temperature overnight. The next day the reaction mixture was diluted with water (5 mL) and extracted with EtOAc (2×10 mL). The combined organic layers were washed with water (20 mL) and brine (20 mL), dried over Na2SO4, and concentrated to obtain a crude oil. Purification of the crude material using silica gel chromatography (gradient of 0% to 100% EtOAc in hexanes) afforded tert-butyl 4-(4-((2-fluoroethoxy)methyl)phenyl)piperazine-1carboxylate as a colorless oil (26 mg, 22% yield). ¹H NMR (300 MHz, CDCl₃) δ 7.27 (d, 2H, J=9.0 Hz), 6.89 (d, 2H, J=9.0 Hz), 4.65 (m, 1H), 4.52 (s, 2H), 4.49 (m, 1H), 3.74 (m, 1H), 3.64 (m, 1H), 3.58 (dd, 4H, J=6.0, 3.0 Hz), 3.13 (dd, 4H, J=6.0, 3.0 Hz), 1.49 (s, 9H); ¹⁹F NMR (282.4 MHz, CDCl₃): δ −223.01 (m, 1F); ¹³C NMR (75.5 MHz, CDCl₃); δ 154.7, 150.9, 129.4, 129.2, 116.5, 84.3 (82.0), 79.9, 73.0, 68.8 (68.7), 49.3, 44.0, 28.4; HRMS calcd for C₁₈H₂₇FN₂O₅: 339.20785 found 339.20790.

Synthesis of 1-(4-((2-fluoroethoxy)methyl)-phenyl)piperazine hydrochloride

Tert-butyl 4-(4-((2-fluoroethoxy)methyl)phenyl)piperazine-1-carboxylate (100 mg, 0.29 mmol) was dissolved in a 4.0M solution of HCl in dioxane (1 mL) and stirred at room temperature. After 1 h, 1-(4-((2-fluoroethoxy)methyl)-phenyl)piperazine hydrochloride was collected as a white solid via filtration (74 mg, 91% yield). ¹H NMR (300 MHz, DMSO-d6): δ 10.45 (br s, 1H), 9.71 (br s, 1H), 7.26 (d, 2H, J=8.7 Hz), 7.05 (d, 2H, J=8.7 Hz), 4.61 (m, 1H), 4.45 (m, 1H), 4.43 (s, 2H), 3.67 (m, 1H), 3.57 (m, 1H), 3.45 (dd, 4H, J=5.5, 4.9 Hz), 3.22 (m, 4H); ¹⁹F NMR (282.4 MHz, CDCl₃): δ −221.40 (m, 1F); ¹³C NMR (75.5 MHz, DMSO): δ 148.5, 130.7, 128.9, 116.4, 84.0 (82.0), 71.7, 68.7 (68.6), 46.0, 42.2; HRMS calcd for C₁₃H₁₉FN₂O: 239.15542 found 239.15540.

Synthesis of 4-(4-((2-fluoroethoxy)methyl)phenyl)piperazine-1-carboximidamide

To a solution of 1-(4-((2-fluoroethoxy)methyl)-phenyl)piperazine hydrochloride (50 mg, 0.12 mmol) and diisopropylethylamine (67 μL, 0.38 mmol) in DMF (1 mL) was added 1H-pyrazole-1-carboximidamide hydrochloride (29 mg, 0.20 mmol). The reaction stirred at room temperature for 24 h. The next day, the reaction mixture was concentrated to yield a crude oil, which was purified via HPLC using a Phenomenex Luna C-18 (2) column (10μ, 250×21.2 mm, gradient method 15-55% B over 20 min., where B=90% ACN in water using 0.1% formic acid as a modifier and A=water using 0.1% formic acid as a modifier) with a flow rate of 20 mL/min afforded 4-(4-((2-fluoroethoxy)methyl)phenyl)piperazine-1-carboximidamide as a white solid (20 mg, 41% yield based on recovered starting material). ¹H NMR (300 MHz, DMSO-d6): δ 7.58 (br s, 4H), 7.211 (d, 2H, J=8.5 Hz), 6.96 (d, 2H, J=8.6 Hz), 4.61 (m, 1H), 4.45 (m, 1H), 4.41 (s, 2H), 3.67 (m, 1H), 3.58 (dd, 4H, J=4.2, 3.9 Hz), 3.22 (m, 5H); ¹⁹F NMR (282.4 MHz, DMSO-d6): δ −221.39 (m, 1F); ¹³C NMR (75.5 MHz, DMSO-d6): δ 156.1, 149.8, 128.9, 115.4, 84.1 (81.9), 71.8, 68.6 (68.4), 47.5, 44.7; HRMS calcd for C₁₄H₂₁FN₄O: 281.177216 found 281.17720.

Example 22 Synthesis of 4-(4-(3-fluoropropyl)phenyl)piperazine-1-carboximidamide

Synthesis of tert-butyl 4-(4-iodophenyl)piperazine-1-carboxylate

To a solution of 4-iodophenylpiperazine hydrochloride (1.0 g, 3.08 mmol) in water (15 mL) was added sodium hydroxide (246 mg, 6.16 mmol), followed by di-tert-butyl dicarbonate (740 mg, 3.39 mmol). The reaction mixture stirred at room temperature overnight. The next day, the reaction mixture was filtered to collect tert-butyl 4-(4-iodophenyl)piperazine-1-carboxylate as a tan solid (1.1 g, 92% yield), which was washed with water (50 mL) and taken on to the next step without further purification. ¹H NMR (600 MHz, CDCl₃): δ 7.53 (d, 2H, J=9.0 Hz), 6.68 (d, 2H, J=9.0 Hz), 3.57 (dd, 4H, J=5.2, 5.0 Hz), 3.11 (dd, 4H, J=4.9, 4.9 Hz), 1.49 (s, 9H); ¹³C NMR (150 MHz, CDCl₃): δ 154.9, 151.1, 138.1, 118.8, 82.3, 80.2, 67.3, 49.2, 28.7; HRMS calcd for C₁₅H₂₁IN₂O₅: 389.07205 found 389.07165.

Synthesis of tert-butyl 4-(4-(3-hydroxyprop-1-ynyl)phenyl)piperazine-1-carboxylate

To a slurry of tert-butyl 4-(4-iodophenyl)piperazine-1-carboxylate (200 mg, 0.515 mmol), triphenylphosphine (1.4 mg, 0.005 mmol), and palladium chloride (0.5 mg, 0.003 mmol) in DEA (2 mL) was added DMF (400 μL) and copper iodide (1 mg, 0.005 mmol). The reaction mixture stirred at room temperature for 24 h. The next day, the reaction mixture was concentrated and purified using silica gel chromatography (gradient method 0%-100% EtOAc in hexanes) to afford tert-butyl 4-(4-(3-hydroxyprop-1-ynyl)phenyl)piperazine-1-carboxylate as a yellow solid (92 mg, 75% yield based on recovered starting material). ¹H NMR (300 MHz, CDCl₃): δ 7.34 (d, 2H, J=8.8 Hz), 6.82 (d, 2H, J=8.9 Hz), 4.48 (d, 2H, J=5.6 Hz), 3.57 (dd, 4H, J=5.5, 4.9 Hz), 3.18 (dd, 4H, J=5.4, 5.0 Hz), 1.87 (t, 1H, J=5.7 Hz), 1.49 (s, 9H); ¹³C NMR (75 MHz, CDCl₃): δ 154.7, 150.9, 132.8, 115.5, 113.1, 85.9, 80.0, 51.7, 48.4, 44.8, 28.4; HRMS calcd for C₁₈H₂₄N₂O₃: 317.18597 found 317.1861.

Synthesis of tert-butyl 4-(4-(3-hydroxypropyl)phenyl)piperazine-1-carboxylate

To a solution of tert-butyl 4-(4-(3-hydroxyprop-1-ynyl)phenyl)piperazine-1-carboxylate (3.2 g, 10.11 mmol) in EtOH (253 mL) was added EtOAc (200) and Pd/C (10% mol on carbon, 3.2 g). The reaction mixture was shaken at 50 psi of H₂ atm. overnight. The next day, the catalyst was removed from the reaction mixture via a filtration over a pad of celite and the filtrate was concentrated to yield a crude oil. Purification of the crude material using silica gel chromatography (gradient method of 0%-100% EtOAc in hexanes) yielded tert-butyl 4-(4-(3-hydroxypropyl)phenyl)piperazine-1-carboxylate as an off-white solid (2.3 g, 71% yield). ¹H NMR (300 MHz, CDCl₃): δ 7.11 (d, 2H, J=8.7 Hz), 6.89 (d, 2H, J=8.7 Hz), 3.67 (br t, 2H, J=6.4 Hz), 3.58 (dd, 4H, J=5.2, 5.1 Hz), 3.09 (dd, 4H, J=5.2, 5.0 Hz), 2.65 (dd, 2H, J=8.0, 7.4 Hz), 1.87 (m, 2H), 1.49 (s, 9H); ¹³C NMR (150 MHz, CDCl₃): δ 154.9, 149.7, 133.9, 129.3, 117.1, 80.1, 62.4, 49.9, 44.1, 34.5, 31.3, 28.6; HRMS calcd for C₁₈H₂₈N₂O₃: 321.21727 found 321.2174.

Synthesis of tert-butyl 4-(4-(3-fluoropropyl)phenyl)piperazine-1-carboxylate

To a solution of deoxofluor (152 μL, 0.69 mmol) in DCM (1.0 mL) at −78° C. was added tert-butyl 4-(4-(3-hydroxypropyl)phenyl)piperazine-1-carboxylate (200 mg, 0.625 mmol) dissolved in DCM (1.0 mL). After stirring at 0° C. for 1 h the reaction mixture was quenched with saturated NaHCO₃, and extracted with DCM (2×5 mL). All combined organic layers were washed with water (10 mL) and brine (10 mL), dried over Na₂SO₄, filtered, and concentrated to obtain a crude oil. The crude material was purified using silica gel chromatography (0%-100% gradient of EtOAc in Hexanes) to obtain tert-butyl 4-(4-(3-fluoropropyl)phenyl)piperazine-1-carboxylate (78 mg, 46% yield was on recovered starting material). ¹H NMR (300 MHz, CDCl₃): δ 7.12 (d, 2H, J=8.7 Hz), 6.89 (d, 2H, J=8.6 Hz), 4.53 (t, 1H, J=6.0 Hz), 4.38 (t, 1H, J=6.0 Hz), 3.59 (dd, 4H, J=5.3, 5.1 Hz), 3.10 (dd, 4H, J=5.2, 5.0 Hz), 2.68 (dd, 2H, J=8.1, 7.2 Hz), 2.07-1.90 (m, 2H), 1.49 (s, 9H); ¹⁹F NMR (282 MHz, CDCl₃): δ −220.02 (m, 1F); ¹³C NMR (75 MHz, CDCl₃): δ 154.9, 149.8, 133.2, 129.4, 117.1, 84.5 (82.3), 80.1, 49.9, 43.9, 32.5 (32.2), 30.6 (30.5), 28.65; HRMS calcd for C₁₈H₂₇FN₂O₂: 323.212933 found 323.21320.

Synthesis of 1-(4-(3-fluoropropyl)phenyl)piperazine

Tert-butyl 4-(4-(3-fluoropropyl)phenyl)piperazine-1-carboxylate (78 mg, 0.24 mmol) was dissolved in a 4.0M solution of HCl in dioxane (3 mL) and stirred at room temperature. After 1 h 1-(4-(3-fluoropropyl)phenyl)piperazine hydrochloride was collected as a white solid via filtration (63 mg). ¹H NMR (300 MHz, CDCl₃): δ 9.58 (br s, 2H), 9.38 (br s, 1H), 7.15 (d, 2H, J=8.7 Hz), 7.00 (d, 2H, J=8.6 Hz), 4.49 (t, 1H, J=6.0 Hz), 4.34 (t, 1H, J=6.0 Hz), 3.40 (dd, 4H, J=5.5, 4.7 Hz), 3.22 (br s, 4H), 2.59 (dd, 2H, J=8.1, 6.3 Hz), 1.98-1.80 (m, 2H); ¹⁹F NMR (282.4 MHz, CDCl₃): δ −217.98 (m, 1F); ¹³C NMR (75.5 MHz, CDCl₃): δ 147.3, 133.6, 128.9, 116.71, 83.6 (82.5), 46.2, 42.2, 31.5 (31.4), 29.7 (29.6); HRMS calcd for C₁₃H₁₉FN₂:223.160503 found 223.16060.

Synthesis of 4-(4-(3-fluoropropyl)phenyl)piperazine-1-carboximidamide

To a solution of 1-(4-(3-fluoropropyl)phenyl)piperazine hydrochloride (50 mg, 0.22 mmol) and diisopropylethylamine (82 μL, 0.47 mmol) in DMF (1 mL) was added 1H-pyrazole-1-carboximidamide hydrochloride (36 mg, 0.25 mmol). After stirring at room temperature for 9 h, the reaction mixture was purified via HPLC using a Phenomenex Luna C-18 (2) column (10μ, 250×21.2 mm, gradient method 15-55% B over 40 min., where B=90% ACN in water using 0.1% TFA as a modifier and A=water using 0.1% TFA as a modifier) with a flow rate of 20 mL/min afforded 4-(4-(3-fluoropropyl)phenyl)piperazine-1-carboximidamide as a white solid (36 mg, 42% yield). ¹H NMR (300 MHz, DMSO-d6): δ 7.53 (br s, 3H), 7.09 (d, 2H, J=8.6 Hz), 6.92 (d, 2H, J=8.6 Hz), 4.50 (t, 1H, J=6.0 Hz), 4.34 (t, 1H, J=6.0 Hz), 3.57 (dd, 4H, J=5.3, 4.8 Hz), 3.17 (dd, 4H, J=5.2, 4.9 Hz), 2.58 (dd, 2H, J=8.1, 6.4 Hz), 1.98-1.80 (m, 2H); ¹⁹F NMR (282.4 MHz, DMSO-d6): δ −217.97 (m, 1F); ¹³C NMR (150 MHz, DMSO-d6): δ 156.1, 148.5, 132.1, 128.8, 116.2, 83.6 (82.5), 47.8, 44.8, 31.7 (31.6), 29.7 (29.6); HRMS calcd. for C₁₄H₂₁FN₄: 265.18230 found 265.18240.

Examples 23 and 24 Synthesis of N-[3-bromo-4-(3-fluoro-propoxy)-benzyl]-guanidine hydrochloride and N-[3-bromo-4-(3-[18F]fluoropropoxy)-benzyl]-guanidine hydrochloride Part A—Synthesis of 3-bromo-4-(tert-butyl-dimethyl-silanyloxy)-benzaldehyde

To a solution of 3-bromo-4-hydroxy-benzaldehyde (7.14 g, 35.52 mmol) dissolved in DMF (35.5 mL) was added imidazole (5.80 g, 85.24 mmol) and TBDMS-Cl (6.42 g, 42.62 mmol). The reaction mixture stirred for 4 h and was then diluted with water (50 mL). The aqueous layer was extracted with EtOAc (3×50 mL). The organic layer was dried over Na₂SO₄ and concentrated to yield a crude oil. Purification using silica gel chromatography afforded 3-bromo-4-(tert-butyl-dimethyl-silanyloxy)-benzaldehyde as a yellow oil (5.13 g, 46% yield). ¹H NMR (CDCl₃, 300 MHz): δ 9.83 (s, 1H), 8.06 (d, J=3.0 Hz, 1H), 7.71 (dd, J=3.0, 9.0 Hz, 1H), 6.97 (d, J=9.0 Hz, 1H), 1.17 (s, 9H), 0.28 (s, 6H); ¹³C NMR (CDCl₃, 75 MHz): δ 189.8, 158.3, 135.5, 131.5, 130.5, 120.2, 116.6, 25.8, 18.6, −4.0.

Part B—Synthesis of [3-bromo-4-(tert-butyl-dimethyl-silanyloxy)-phenyl]-methanol

To a cooled (0° C.) solution of 3-bromo-4-(tert-butyl-dimethyl-silanyloxy)-benzaldehyde (5.13 g, 16.33 mmol) dissolved in MeOH (16.5 mL) was added Na₂BH₄ (0.309 g, 8.17 mmol) portion-wise. Once all the reducing agent was added the reaction mixture stirred at room temperature for 30 minutes before being quenched with water (15 mL). MeOH was removed en vacuo and DCM (20 mL) was added to the remaining crude reaction mixture. The aqueous layer was extracted with DCM (3×20 mL). Combined organics were dried over Mg₂SO₄ and concentrated to yield a crude oil. Purification using silica gel chromatography afforded [3-bromo-4-(tert-butyl-dimethyl-silanyloxy)-phenyl]-methanol as a colorless oil (4.22 g, 82% yield). ¹H NMR (CDCl₃, 300 MHz): δ 7.55 (m, 1H), 7.17 (dd, J=3.0, 9.0 Hz, 1H), 6.86 (d, J=9.0 Hz, 1H), 4.61 (s, 2H), 1.05 (s, 9H), 0.26 (s, 6H); ¹³C NMR (CDCl₃, 75 MHz): δ 152.4, 135.3, 132.5, 127.3, 120.5, 115.6, 64.6, 26.0, 18.6, −4.0.

Part C—Synthesis of 1,3-bis(tert-butoxy-carbonyl)-[3-bromo-4-(tert-butyl-dimethyl-silanyloxy)-benzyl]-guanidine

To a solution of [3-bromo-4-(tert-butyl-dimethyl-silanyloxy)-phenyl]-methanol (3.11 g, 9.84 mmol) dissolved in THF (98.4 mL) was added PPh₃ (3.87 g, 14.76 mmol), 1,3 bis(tert-butoxy-carbonyl)guanidine (3.83 g, 11.81), and DIAD (2.86 mL, 14.76 mmol). The reaction mixture stirred at room temperature for 30 minutes before being concentrated en vacuo. The resulting yellow oil was purified using silica gel chromatography (4:1 hexanes: EtOAc) to afford 1,3-bis(tert-butoxy-carbonyl)-[3-bromo-4-(tert-butyl-dimethyl-silanyloxy)-benzyl]-guanidine (5.14 g, 94% yield). ^(1H) NMR (CDCl₃, 300 MHz): δ 9.48 (br s, 2H), 7.48 (m, 1H), 7.12 (dd, J=3.0, 9.0 Hz, 1H), 6.80 (d, J=9.0 Hz, 1H), 5.07 (s, 2H), 1.55 (s, 9H)¹1.34 (s, 9H), 1.03 (s, 9H), 0.24 (s, 6H); ¹³C NMR (CDCl₃, 75 MHz): δ 155.0, 151.8, 133.3, 133.0, 127.7, 120.2, 115.0, 84.6, 46.8, 28.5, 28.1, 26.0, 18.6, −4.0.

Part D—Synthesis of 1,3-bis(tert-butoxy-carbonyl)-[3-bromo-4-hydroxy-benzyl]-guanidine

To a solution of AA (5.14 g, 9.22 mmol) dissolved in THF (92.2 mL) was added a solution of TBAF (18.56 mL of 1M THF solution, 18.46 mmol) drop-wise. After completion of addition the reaction mixture continued to stir at room temperature for 20 minutes. The reaction mixture was concentrated en vacuo to yield a crude oil, which was purified using silica gel chromatography (4:1 hexanes:EtOAc) to afford a white solid (3.52 g, 88% yield). ¹H NMR (CDCl₃, 300 MHz): δ 9.48 (br s, 2H), 7.45 (m, 1H), 7.15 (dd, J=3.0, 9.0 Hz, 1H), 6.92 (d, J=9.0 Hz, 1H), 5.08 (s, 2H), 1.52 (s, 9H) 1.42 (s, 9H).

Part E—Synthesis of 1,3-bis(tert-butoxy-carbonyl-[3-bromo-4-(3-fluoro-propoxy)-benzyl]-guanidine

To a solution of phenol (300 mg, 0.677 mmol) dissolved in DMF (7 mL) was added 1-bromo-3-fluoro propane (123.16 mg, 0.880 mmol) and K₂CO₃ (140.3 mg, 1.02 mmol). The reaction mixture was heated to 50 C for 2.5 h before being quenched with water (10 mL). The aqueous layer was extracted with EtOAc (20 mL). Organic layer was dried over Na₂SO₄, filtered, and concentrated to yield a yellow oil. Purification of the crude material using silica gel chromatography afforded 1,3-bis(tert-butoxy-carbonyl-[3-bromo-4-(3-fluoro-propoxy)-benzyl]-guanidine (208.5 mg, 61% yield). ¹H NMR (CDCl₃, 600 MHz): δ 9.43 (br s, 2H), 7.54 (m, 1H), 7.54 (d, J=7.8 Hz, 1H), 6.84 (d, J=8.4 Hz, 1H), 5.09 (s, 2H), 4.74 (m, 1H), 4.67 (m, 1H), 4.14 (m, 1H), 2.26-2.18 (m, 2H), 1.51 (s, 9H) 1.42 (s, 9H); ¹³C NMR (CDCl₃, 150 MHz): δ 155.0, 154.4, 133.2, 128.1, 113.2, 111.9, 81.4 (80.3), 65.0 (64.9), 46.8, 30.7 (30.5), 28.5, 28.0; ¹⁹F NMR (CDCl₃, 282 MHz): δ −222.68 (m, 1F).

Part F—Example 23—Synthesis of N-[3-bromo-4-(3-fluoro-propoxy)-benzyl]-guanidine hydrochloride

A solution of 1,3-bis(tert-butoxy-carbonyl-[3-bromo-4-(3-fluoro-propoxy)-benzyl]-guanidine (250.6 mg, 50 mmol) in 4N HCl in dioxane (6 mL) was heated to 50° C. for 2 h. The reaction mixture was diluted with water (4 mL) and ACN (1 mL) and lyophilized to afford N-[3-bromo-4-(3-fluoro-propoxy)-benzyl]-guanidine hydrochloride as a white solid (169.1 mg, 99% yield). ¹H NMR (DMSO-d6, 600 MHz): δ 8.03 (br t, 1H), 7.55 (m, 1H), 7.31-7.27 (m, 2H), 7.15 (d, J=9 Hz, 1H), 4.72 (t, J=6 Hz, 1H), 4.56 (t, J=6 Hz, 1H), 4.30 (m, 2H), 4.15 (t, J=6 Hz, 2H), 2.19-2.06 (m, 2H).

Part G—Example 24—Synthesis of N-[3-bromo-4-(3-[18F]fluoropropoxy)-benzyl]-guanidine hydrochloride

To a solution of phenol (3 mg, 6.77 umol) dissolved in acetonitrile (0.7 mL) was added 3-[18F]fluoropropyl toluenesulfonate (350 uCi) and K₂CO₃ (1.40 mg). The reaction mixture was heated to 80° C. for 45 minutes and cooled to room temperature. The solvent was evaporated in a stream of warm nitrogen under partial vacuum. 4N HCl in dioxane (1.0 mL) was added and the resultant mixture was heated to 50° C. for 15 minutes. The reaction mixture was diluted with water (15 mL) deposited onto a reverse-phase (C-18) cartridge. The salts were removed by washing the column with distilled water, and the compound was eluted with pure acetonitrile (2.0 mL). An aliquot was purified via reversed phase HPLC to afford a ca. 10 mCi sample of pure N-[3-bromo-4-(3-[18F]fluoropropoxy)-benzyl]-guanidine hydrochloride.

Example 25—Animal Preparation

Male Sprague Dawley rats (300-500 g, Taconic), male New Zealand rabbits (3-4 kg, Covance) and male non-human primates (NHP, Cynomolgus monkeys 2-4 kg) were used in this study in concordance with our Institutional Animal Care and Use Committee. In tissue biodistribution and imaging studies, rats were anesthetized with sodium pentobarbital (50 mg/kg, i.p.) and the left femoral vein was canulated with PE50 tubing for drug injection. Rabbits were pre-sedated with acepromazine (0.75 mg/kg i.m.) and then anesthetized with ketamine (40 mg/kg, i.m.) and xylazine (8 mg/kg, i.m). The ear marginal vein was canulated for drug injection. NHPs were anesthetized with acepromazine (0.3 mg/kg, i.m.) and ketamine (10 mg/kg, i.m.), orally intubated and maintained with isoflurane (0.4-1.5%). The saphenous vein in the legs was canulated for drug injection. Additional doses of anesthetics were given as needed.

Tissue Biodistribution in Rats and Rabbits

After anesthesia and vein canulation, each animal received a bolus injection of ¹⁸F labeled agent via the venous catheter. Rats and rabbits were euthanized after the injection and samples of the blood, heart, lung, liver, spleen, kidney, femur and muscle were collected. All samples were weighed and counted for radioactivity (Wallac Wizard 1480, PerkinElmer Life and Analytical Sciences, Shelton, Conn.). The net amount of activity administered in each animal was calculated by subtracting the residual activities in the syringe and venous catheter. The tissue uptake of each agent was determined as % injected dose per gram tissue (% ID/g).

Cardiac PET Imaging in Animals

Cardiac PET imaging was performed in anesthetized rats, rabbits and NHP. Each animal was anesthetized and a venous catheter was established for imaging agent injection. Then the animal was positioned in a microPET camera (Focus220, CTI Molecular Imaging, Inc. Knoxville, Tenn.) for cardiac imaging. Labeled agent was injected intravenously and animals imaged up to 120 minutes.

Image Reconstruction and Analysis

After the acquisition, images were reconstructed in a matrix of 256×256 pixels with 95 transverse slices using the filtered back projection algorithm and decay corrected (microPET Manager and ASIPro, CTI Molecular Imaging, Inc. Knoxville, Tenn.). The pixel size was 0.47 mm and the slice thickness was 0.80 mm. The images were reoriented regarding cardiac axis and serial tomographic cardiac image frames were then generated for every 10-minute period from 5 to 125 minutes.

FIGS. 1 and 2 represent the images derived from cardiac scanning according to the invention.

All publications and patents mentioned in the above specification are herein incorporated by reference. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention that are obvious to those skilled in the relevant fields are intended to be within the scope of the following claims. 

What is claimed is:
 1. A compound having Structure Chi as follows:

or a salt thereof; wherein R selected from the group consisting of OR₃, OCH₂CH₂F, and OCH₂CH₂Im; R₁ is selected from the group consisting of H, OR₃, F, Cl, Br, and I; and R₂ is H; R₃ is alkyl; wherein said alkyl, of R₃ is substituted with one or more groups selected from halogen, Im, COOR₄, CON(R₄)₂,SR₄, OR₄, and NHC(=O)NH₂; R₄ is alkyl; and wherein Im is an imaging agent selected from the group consisting of ¹⁸F, ⁷⁶Br, ¹²⁴I, and ¹³¹I.
 2. The compound of claim 1, wherein the alkyl group is substituted with a functional group selected from the group consisting of F, Cl, Br, I, Im, COOR₄, CON(R₄)₂, SR₄, OR₄and NHC(=O)NH2.
 3. The compound of claim 1, wherein Im is ¹⁸F.
 4. A compound of the formula:

or a pharmaceutically acceptable salt thereof. 